diff --git a/apps/server/src/application/coordinators/coordinatorDeps.ts b/apps/server/src/application/coordinators/coordinatorDeps.ts
new file mode 100644
index 0000000..1092676
--- /dev/null
+++ b/apps/server/src/application/coordinators/coordinatorDeps.ts
@@ -0,0 +1,32 @@
+/**
+ * coordinatorDeps
+ * コーディネータが利用する依存束ね型を定義する
+ */
+import type {
+  CleanupGameRuntimePort,
+  DisconnectRoomPort,
+  FindGameByPlayerPort,
+  FindGameByRoomPort,
+  FindRoomByIdPort,
+  FindRoomByOwnerPort,
+  FindRoomByPlayerPort,
+  RoomPhaseTransitionPort,
+} from "@server/domains/room/application/ports/roomUseCasePorts";
+
+/** START_GAME調停で利用する依存集合 */
+export type StartGameCoordinatorDeps = {
+  roomManager: FindRoomByOwnerPort & RoomPhaseTransitionPort;
+  runtimeRegistry: FindGameByRoomPort;
+};
+
+/** READY_FOR_GAME調停で利用する依存集合 */
+export type ReadyForGameCoordinatorDeps = {
+  roomManager: FindRoomByPlayerPort;
+  runtimeRegistry: FindGameByPlayerPort;
+};
+
+/** DISCONNECT調停で利用する依存集合 */
+export type DisconnectCoordinatorDeps = {
+  roomManager: DisconnectRoomPort & FindRoomByPlayerPort & FindRoomByIdPort;
+  runtimeRegistry: FindGameByPlayerPort & CleanupGameRuntimePort;
+};
diff --git a/apps/server/src/application/coordinators/disconnectCoordinator.ts b/apps/server/src/application/coordinators/disconnectCoordinator.ts
index fdcfc85..acd27c8 100644
--- a/apps/server/src/application/coordinators/disconnectCoordinator.ts
+++ b/apps/server/src/application/coordinators/disconnectCoordinator.ts
@@ -5,10 +5,8 @@
 import {
   type GameOutputPort,
 } from "@server/domains/game/application/ports/gameUseCasePorts";
-import type {
-  DisconnectDeps,
-  RoomOutputPort,
-} from "@server/domains/room/application/ports/roomUseCasePorts";
+import type { RoomOutputPort } from "@server/domains/room/application/ports/roomUseCasePorts";
+import type { DisconnectCoordinatorDeps } from "./coordinatorDeps";
 import { resolveRuntimeByPlayerId } from "@server/domains/room/application/services/RoomRuntimeResolver";
 import { disconnectUseCase } from "@server/domains/game/application/useCases/disconnectUseCase";
 import { roomDisconnectUseCase } from "@server/domains/room/application/useCases/roomDisconnectUseCase";
@@ -16,7 +14,7 @@
 /** 切断調停で利用する入力ポートと出力ポートの契約 */
 export type DisconnectCoordinatorParams = {
   socketId: string;
-} & DisconnectDeps & {
+} & DisconnectCoordinatorDeps & {
   gameOutput: Pick<GameOutputPort, "publishPlayerRemovedToRoom">;
   roomOutput: Pick<RoomOutputPort, "publishRoomUpdateToRoom">;
 };
diff --git a/apps/server/src/application/coordinators/readyForGameCoordinator.ts b/apps/server/src/application/coordinators/readyForGameCoordinator.ts
index 68d8f44..897a981 100644
--- a/apps/server/src/application/coordinators/readyForGameCoordinator.ts
+++ b/apps/server/src/application/coordinators/readyForGameCoordinator.ts
@@ -5,13 +5,13 @@
 import {
   type GameOutputPort,
 } from "@server/domains/game/application/ports/gameUseCasePorts";
-import type { ReadyForGameDeps } from "@server/domains/room/application/ports/roomUseCasePorts";
+import type { ReadyForGameCoordinatorDeps } from "./coordinatorDeps";
 import { resolveRuntimeByPlayerId } from "@server/domains/room/application/services/RoomRuntimeResolver";
 import { readyForGameUseCase } from "@server/domains/game/application/useCases/readyForGameUseCase";
 
 type ReadyForGameCoordinatorParams = {
   socketId: string;
-} & ReadyForGameDeps & {
+} & ReadyForGameCoordinatorDeps & {
   output: Pick<GameOutputPort, "publishCurrentPlayersToSocket" | "publishGameStartToSocket">;
 };
 
diff --git a/apps/server/src/application/coordinators/startGameCoordinator.ts b/apps/server/src/application/coordinators/startGameCoordinator.ts
index 75198dd..7e835ba 100644
--- a/apps/server/src/application/coordinators/startGameCoordinator.ts
+++ b/apps/server/src/application/coordinators/startGameCoordinator.ts
@@ -5,17 +5,14 @@
 import {
   type GameOutputPort,
 } from "@server/domains/game/application/ports/gameUseCasePorts";
-import type {
-  StartGameDeps,
-} from "@server/domains/room/application/ports/roomUseCasePorts";
+import type { StartGameCoordinatorDeps } from "./coordinatorDeps";
 import { startGameUseCase } from "@server/domains/game/application/useCases/startGameUseCase";
 import { logEvent } from "@server/logging/logger";
 import { gameUseCaseLogEvents, logResults, logScopes } from "@server/logging/index";
-import { roomConsts } from "@repo/shared";
 
 type StartGameCoordinatorParams = {
   ownerId: string;
-} & StartGameDeps & {
+} & StartGameCoordinatorDeps & {
   output: Pick<
     GameOutputPort,
     | "publishUpdatePlayersToSocket"
@@ -43,7 +40,18 @@
     return;
   }
 
-  if (room.status === roomConsts.RoomPhase.PLAYING) {
+  const transitionResult = roomManager.markRoomPlaying(room.roomId);
+  if (transitionResult.status === "not_found") {
+    logEvent(logScopes.GAME_USE_CASE, {
+      event: gameUseCaseLogEvents.START_GAME,
+      result: logResults.IGNORED_ROOM_NOT_FOUND,
+      roomId: room.roomId,
+      socketId: ownerId,
+    });
+    return;
+  }
+
+  if (transitionResult.status === "invalid_transition") {
     logEvent(logScopes.GAME_USE_CASE, {
       event: gameUseCaseLogEvents.START_GAME,
       result: logResults.IGNORED_ALREADY_PLAYING,
@@ -53,14 +61,8 @@
     return;
   }
 
-  const updatedRoom = roomManager.markRoomPlaying(room.roomId);
+  const updatedRoom = transitionResult.room;
   if (!updatedRoom) {
-    logEvent(logScopes.GAME_USE_CASE, {
-      event: gameUseCaseLogEvents.START_GAME,
-      result: logResults.IGNORED_ROOM_NOT_FOUND,
-      roomId: room.roomId,
-      socketId: ownerId,
-    });
     return;
   }
 
diff --git a/apps/server/src/domains/room/RoomManager.ts b/apps/server/src/domains/room/RoomManager.ts
index 4205a81..fc446c6 100644
--- a/apps/server/src/domains/room/RoomManager.ts
+++ b/apps/server/src/domains/room/RoomManager.ts
@@ -7,7 +7,11 @@
 import { RoomExitService } from "./application/services/RoomExitService";
 import { RoomPhaseService } from "./application/services/RoomPhaseService";
 import { RoomQueryService } from "./application/services/RoomQueryService";
-import type { JoinRoomResult } from "./application/ports/roomUseCasePorts";
+import type {
+  JoinRoomResult,
+  RoomDisconnectResult,
+  RoomPhaseTransitionResult,
+} from "./application/ports/roomUseCasePorts";
 
 /** ルーム操作の公開インターフェースを提供するマネージャ */
 export class RoomManager {
@@ -30,7 +34,7 @@
   }
 
   // プレイヤーをルームから削除し，更新が発生したルーム配列を返す
-  public removePlayer(socketId: string): roomTypes.Room[] {
+  public removePlayer(socketId: string): RoomDisconnectResult {
     return this.roomExitService.removePlayer(socketId);
   }
 
@@ -50,12 +54,12 @@
   }
 
   // ルーム状態をPLAYINGへ更新する
-  public markRoomPlaying(roomId: string): roomTypes.Room | undefined {
+  public markRoomPlaying(roomId: string): RoomPhaseTransitionResult {
     return this.roomPhaseService.markRoomPlaying(roomId);
   }
 
   // ルーム状態をWAITINGへ更新する
-  public markRoomWaiting(roomId: string): roomTypes.Room | undefined {
+  public markRoomWaiting(roomId: string): RoomPhaseTransitionResult {
     return this.roomPhaseService.markRoomWaiting(roomId);
   }
 }
\ No newline at end of file
diff --git a/apps/server/src/domains/room/application/ports/roomUseCasePorts.ts b/apps/server/src/domains/room/application/ports/roomUseCasePorts.ts
index 034ee0d..f727fcb 100644
--- a/apps/server/src/domains/room/application/ports/roomUseCasePorts.ts
+++ b/apps/server/src/domains/room/application/ports/roomUseCasePorts.ts
@@ -38,9 +38,15 @@
 
 /** ルーム切断ユースケースが利用する退出操作ポート */
 export interface DisconnectRoomPort {
-  removePlayer(socketId: string): roomTypes.Room[];
+  removePlayer(socketId: string): RoomDisconnectResult;
 }
 
+/** 退出処理で更新対象となったルーム情報 */
+export type RoomDisconnectResult = {
+  updatedRooms: roomTypes.Room[];
+  deletedRoomIds: string[];
+};
+
 /** 切断調停で利用するプレイヤー所属ルーム参照ポート */
 export interface FindRoomByPlayerPort {
   getRoomByPlayerId(playerId: string): roomTypes.Room | undefined;
@@ -53,10 +59,16 @@
 
 /** ゲーム開始調停で利用するルーム状態遷移ポート */
 export interface RoomPhaseTransitionPort {
-  markRoomPlaying(roomId: string): roomTypes.Room | undefined;
-  markRoomWaiting(roomId: string): roomTypes.Room | undefined;
+  markRoomPlaying(roomId: string): RoomPhaseTransitionResult;
+  markRoomWaiting(roomId: string): RoomPhaseTransitionResult;
 }
 
+/** ルーム状態遷移の実行結果 */
+export type RoomPhaseTransitionResult = {
+  status: "updated" | "not_found" | "invalid_transition";
+  room?: roomTypes.Room;
+};
+
 /** ルームIDでの存在確認に利用する参照ポート */
 export interface FindRoomByIdPort {
   getRoomById(roomId: string): roomTypes.Room | undefined;
@@ -81,21 +93,3 @@
 export interface FindGameByPlayerPort {
   getGameManagerByPlayerId(playerId: string): RoomScopedGamePort | undefined;
 }
-
-/** START_GAME調停で利用する依存集合 */
-export type StartGameDeps = {
-  roomManager: FindRoomByOwnerPort & RoomPhaseTransitionPort;
-  runtimeRegistry: FindGameByRoomPort;
-};
-
-/** READY_FOR_GAME調停で利用する依存集合 */
-export type ReadyForGameDeps = {
-  roomManager: FindRoomByPlayerPort;
-  runtimeRegistry: FindGameByPlayerPort;
-};
-
-/** DISCONNECT調停で利用する依存集合 */
-export type DisconnectDeps = {
-  roomManager: DisconnectRoomPort & FindRoomByPlayerPort & FindRoomByIdPort;
-  runtimeRegistry: FindGameByPlayerPort & CleanupGameRuntimePort;
-};
diff --git a/apps/server/src/domains/room/application/services/RoomExitService.ts b/apps/server/src/domains/room/application/services/RoomExitService.ts
index 15a3e64..1c54f38 100644
--- a/apps/server/src/domains/room/application/services/RoomExitService.ts
+++ b/apps/server/src/domains/room/application/services/RoomExitService.ts
@@ -3,6 +3,7 @@
  * ルーム退出処理とオーナー移譲処理を担うサービス
  */
 import type { roomTypes } from "@repo/shared";
+import type { RoomDisconnectResult } from "../ports/roomUseCasePorts";
 import { logEvent } from "@server/logging/logger";
 import { logResults, logScopes, roomDomainLogEvents } from "@server/logging/index";
 
@@ -10,8 +11,9 @@
 export class RoomExitService {
   constructor(private rooms: Map<string, roomTypes.Room>) {}
 
-  public removePlayer(socketId: string): roomTypes.Room[] {
+  public removePlayer(socketId: string): RoomDisconnectResult {
     const updatedRooms: roomTypes.Room[] = [];
+    const deletedRoomIds: string[] = [];
 
     for (const [roomId, room] of this.rooms.entries()) {
       const playerIndex = room.players.findIndex((player) => player.id === socketId);
@@ -30,6 +32,7 @@
 
       if (room.players.length === 0) {
         this.rooms.delete(roomId);
+        deletedRoomIds.push(roomId);
         logEvent(logScopes.ROOM_EXIT_SERVICE, {
           event: roomDomainLogEvents.ROOM_DELETE,
           result: logResults.DELETED,
@@ -54,6 +57,9 @@
       updatedRooms.push(room);
     }
 
-    return updatedRooms;
+    return {
+      updatedRooms,
+      deletedRoomIds,
+    };
   }
 }
diff --git a/apps/server/src/domains/room/application/services/RoomPhaseService.ts b/apps/server/src/domains/room/application/services/RoomPhaseService.ts
index 997c27a..b79a237 100644
--- a/apps/server/src/domains/room/application/services/RoomPhaseService.ts
+++ b/apps/server/src/domains/room/application/services/RoomPhaseService.ts
@@ -4,28 +4,49 @@
  */
 import { roomConsts } from "@repo/shared";
 import type { roomTypes } from "@repo/shared";
+import type { RoomPhaseTransitionResult } from "../ports/roomUseCasePorts";
 
 /** ルーム状態のフェーズ遷移を管理するサービス */
 export class RoomPhaseService {
   constructor(private rooms: Map<string, roomTypes.Room>) {}
 
-  public markRoomPlaying(roomId: string): roomTypes.Room | undefined {
+  public markRoomPlaying(roomId: string): RoomPhaseTransitionResult {
     const room = this.rooms.get(roomId);
     if (!room) {
-      return undefined;
+      return { status: "not_found" };
+    }
+
+    if (room.status === roomConsts.RoomPhase.PLAYING) {
+      return {
+        status: "invalid_transition",
+        room,
+      };
     }
 
     room.status = roomConsts.RoomPhase.PLAYING;
-    return room;
+    return {
+      status: "updated",
+      room,
+    };
   }
 
-  public markRoomWaiting(roomId: string): roomTypes.Room | undefined {
+  public markRoomWaiting(roomId: string): RoomPhaseTransitionResult {
     const room = this.rooms.get(roomId);
     if (!room) {
-      return undefined;
+      return { status: "not_found" };
+    }
+
+    if (room.status === roomConsts.RoomPhase.WAITING) {
+      return {
+        status: "invalid_transition",
+        room,
+      };
     }
 
     room.status = roomConsts.RoomPhase.WAITING;
-    return room;
+    return {
+      status: "updated",
+      room,
+    };
   }
 }
diff --git a/apps/server/src/domains/room/application/useCases/roomDisconnectUseCase.ts b/apps/server/src/domains/room/application/useCases/roomDisconnectUseCase.ts
index 6c395ba..61b9a11 100644
--- a/apps/server/src/domains/room/application/useCases/roomDisconnectUseCase.ts
+++ b/apps/server/src/domains/room/application/useCases/roomDisconnectUseCase.ts
@@ -5,15 +5,13 @@
 import type {
   CleanupGameRuntimePort,
   DisconnectRoomPort,
-  FindRoomByIdPort,
-  FindRoomByPlayerPort,
 } from "../ports/roomUseCasePorts";
 import type { RoomOutputPort } from "../ports/roomUseCasePorts";
 import { logEvent } from "@server/logging/logger";
 import { logResults, logScopes, roomUseCaseLogEvents } from "@server/logging/index";
 
 type RoomDisconnectUseCaseParams = {
-  roomManager: DisconnectRoomPort & FindRoomByPlayerPort & FindRoomByIdPort;
+  roomManager: DisconnectRoomPort;
   runtimeRegistry: CleanupGameRuntimePort;
   socketId: string;
   output: Pick<RoomOutputPort, "publishRoomUpdateToRoom">;
@@ -26,8 +24,7 @@
   socketId,
   output,
 }: RoomDisconnectUseCaseParams) => {
-  const beforeRoomId = roomManager.getRoomByPlayerId(socketId)?.roomId;
-  const updatedRooms = roomManager.removePlayer(socketId);
+  const { updatedRooms, deletedRoomIds } = roomManager.removePlayer(socketId);
   logEvent(logScopes.ROOM_USE_CASE, {
     event: roomUseCaseLogEvents.DISCONNECT,
     result: logResults.PROCESSED,
@@ -47,11 +44,7 @@
     });
   });
 
-  if (!beforeRoomId) {
-    return;
-  }
-
-  if (!roomManager.getRoomById(beforeRoomId)) {
-    runtimeRegistry.cleanupGameManagerForRoom(beforeRoomId);
-  }
+  deletedRoomIds.forEach((roomId) => {
+    runtimeRegistry.cleanupGameManagerForRoom(roomId);
+  });
 };
diff --git a/apps/server/src/network/types/connectionPorts.ts b/apps/server/src/network/types/connectionPorts.ts
index dbaf4bc..49454e8 100644
--- a/apps/server/src/network/types/connectionPorts.ts
+++ b/apps/server/src/network/types/connectionPorts.ts
@@ -4,8 +4,10 @@
  */
 import type { Server } from "socket.io";
 import type {
+  DisconnectCoordinatorDeps,
+} from "@server/application/coordinators/coordinatorDeps";
+import type {
   CleanupGameRuntimePort,
-  DisconnectDeps,
   DisconnectRoomPort,
   EnsureGameRuntimePort,
   FindGameByRoomPort,
@@ -42,7 +44,7 @@
   & CleanupGameRuntimePort;
 
 /** ソケット接続ハンドラで受け取るマネージャ依存の束 */
-export type SocketConnectionManagerBundle = DisconnectDeps & {
+export type SocketConnectionManagerBundle = DisconnectCoordinatorDeps & {
   roomManager: SocketConnectionRoomPort;
   runtimeRegistry: SocketConnectionRuntimePort;
 };