diff --git a/apps/client/src/hooks/useAppFlow.ts b/apps/client/src/hooks/useAppFlow.ts
index c6ffc5d..d4359fc 100644
--- a/apps/client/src/hooks/useAppFlow.ts
+++ b/apps/client/src/hooks/useAppFlow.ts
@@ -35,7 +35,8 @@
 
 type JoinFailureReason =
   | domain.room.JoinRoomRejectedPayload["reason"]
-  | "timeout";
+  | "timeout"
+  | "playing";
 
 type JoinFailure = {
   reason: JoinFailureReason;
@@ -119,6 +120,10 @@
         return `ルーム ${joinFailure.roomId ?? ""} は満員です`;
       }
 
+      if (joinFailure.reason === "playing") {
+        return `ルーム ${joinFailure.roomId ?? ""} はゲーム中のため参加できません`;
+      }
+
       if (joinFailure.reason === "duplicate") {
         return `ルーム ${joinFailure.roomId ?? ""} への参加要求が重複しました`;
       }
diff --git a/apps/server/src/application/coordinators/startGameCoordinator.ts b/apps/server/src/application/coordinators/startGameCoordinator.ts
index dc67565..4f0304c 100644
--- a/apps/server/src/application/coordinators/startGameCoordinator.ts
+++ b/apps/server/src/application/coordinators/startGameCoordinator.ts
@@ -106,7 +106,7 @@
     gameSession: gameManager,
     bombStore: gameManager,
     onGameEnd: () => {
-      roomManager.markRoomWaiting(updatedRoom.roomId);
+      roomManager.markRoomResult(updatedRoom.roomId);
     },
     output,
   });
diff --git a/apps/server/src/domains/room/RoomManager.ts b/apps/server/src/domains/room/RoomManager.ts
index 6a7be2e..bacbff0 100644
--- a/apps/server/src/domains/room/RoomManager.ts
+++ b/apps/server/src/domains/room/RoomManager.ts
@@ -58,6 +58,11 @@
     return this.roomPhaseService.markRoomPlaying(roomId);
   }
 
+  // ルーム状態をRESULTへ更新する
+  public markRoomResult(roomId: string): RoomPhaseTransitionResult {
+    return this.roomPhaseService.markRoomResult(roomId);
+  }
+
   // ルーム状態をWAITINGへ更新する
   public markRoomWaiting(roomId: string): RoomPhaseTransitionResult {
     return this.roomPhaseService.markRoomWaiting(roomId);
diff --git a/apps/server/src/domains/room/application/ports/roomUseCasePorts.ts b/apps/server/src/domains/room/application/ports/roomUseCasePorts.ts
index 8826220..14d52ce 100644
--- a/apps/server/src/domains/room/application/ports/roomUseCasePorts.ts
+++ b/apps/server/src/domains/room/application/ports/roomUseCasePorts.ts
@@ -26,7 +26,7 @@
 /** ルーム参加処理の実行結果 */
 export type JoinRoomResult = {
   room: domain.room.Room;
-  status: "joined" | "duplicate" | "full";
+  status: "joined" | "duplicate" | "full" | "playing";
 };
 
 /** ルームユースケースが利用する出力ポート */
@@ -64,6 +64,7 @@
 /** 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): RoomPhaseTransitionResult;
+  markRoomResult(roomId: string): RoomPhaseTransitionResult;
   markRoomWaiting(roomId: string): RoomPhaseTransitionResult;
 }
 
diff --git a/apps/server/src/domains/room/application/services/RoomJoinService.ts b/apps/server/src/domains/room/application/services/RoomJoinService.ts
index 8b72619..979b5b2 100644
--- a/apps/server/src/domains/room/application/services/RoomJoinService.ts
+++ b/apps/server/src/domains/room/application/services/RoomJoinService.ts
@@ -32,6 +32,17 @@
       });
     }
 
+    // 待機中以外のルームへの参加を拒否する
+    if (room.status !== domain.room.RoomPhase.WAITING) {
+      logEvent(logScopes.ROOM_JOIN_SERVICE, {
+        event: roomDomainLogEvents.PLAYER_JOIN,
+        result: logResults.REJECTED_ROOM_PLAYING,
+        roomId,
+        socketId,
+      });
+      return { room, status: "playing" };
+    }
+
     // 同一ソケットの重複参加を防止する
     const alreadyJoined = room.players.some((player) => player.id === socketId);
     if (alreadyJoined) {
diff --git a/apps/server/src/domains/room/application/services/RoomPhaseService.ts b/apps/server/src/domains/room/application/services/RoomPhaseService.ts
index 3ee0466..f28de2f 100644
--- a/apps/server/src/domains/room/application/services/RoomPhaseService.ts
+++ b/apps/server/src/domains/room/application/services/RoomPhaseService.ts
@@ -29,6 +29,26 @@
     };
   }
 
+  public markRoomResult(roomId: string): RoomPhaseTransitionResult {
+    const room = this.rooms.get(roomId);
+    if (!room) {
+      return { status: "not_found" };
+    }
+
+    if (room.status !== domain.room.RoomPhase.PLAYING) {
+      return {
+        status: "invalid_transition",
+        room,
+      };
+    }
+
+    room.status = domain.room.RoomPhase.RESULT;
+    return {
+      status: "updated",
+      room,
+    };
+  }
+
   public markRoomWaiting(roomId: string): RoomPhaseTransitionResult {
     const room = this.rooms.get(roomId);
     if (!room) {
diff --git a/apps/server/src/logging/constants/results.ts b/apps/server/src/logging/constants/results.ts
index f5ff65f..6ab8c75 100644
--- a/apps/server/src/logging/constants/results.ts
+++ b/apps/server/src/logging/constants/results.ts
@@ -28,6 +28,7 @@
   REJECTED: "rejected",
   REJECTED_DUPLICATE: "rejected_duplicate",
   REJECTED_ROOM_FULL: "rejected_room_full",
+  REJECTED_ROOM_PLAYING: "rejected_room_playing",
   REMOVED: "removed",
   SESSION_DISPOSED_EMPTY_ROOM: "session_disposed_empty_room",
   STARTED: "started",
diff --git a/apps/server/src/logging/contracts/payloadByScope.ts b/apps/server/src/logging/contracts/payloadByScope.ts
index 8620418..044d3d0 100644
--- a/apps/server/src/logging/contracts/payloadByScope.ts
+++ b/apps/server/src/logging/contracts/payloadByScope.ts
@@ -27,6 +27,7 @@
   result:
     | typeof logResults.REJECTED_ROOM_FULL
     | typeof logResults.REJECTED_DUPLICATE
+    | typeof logResults.REJECTED_ROOM_PLAYING
     | typeof logResults.IGNORED_INVALID_PAYLOAD
     | typeof logResults.IGNORED_MISSING_ROOM;
   socketId: string;
@@ -224,6 +225,7 @@
   result:
     | typeof logResults.IGNORED_DUPLICATE
     | typeof logResults.IGNORED_ROOM_FULL
+    | typeof logResults.REJECTED_ROOM_PLAYING
     | typeof logResults.JOINED;
   roomId: string;
   socketId: string;
diff --git a/apps/server/src/network/handlers/room/roomEventOrchestrators.ts b/apps/server/src/network/handlers/room/roomEventOrchestrators.ts
index b3b4996..4fbd750 100644
--- a/apps/server/src/network/handlers/room/roomEventOrchestrators.ts
+++ b/apps/server/src/network/handlers/room/roomEventOrchestrators.ts
@@ -49,6 +49,15 @@
       });
       return;
 
+    case "playing":
+      logEvent(logScopes.NETWORK, {
+        event: roomUseCaseLogEvents.JOIN_ROOM,
+        result: logResults.REJECTED_ROOM_PLAYING,
+        roomId: payload.roomId,
+        socketId: deps.socketId,
+      });
+      return;
+
     case "duplicate":
       logEvent(logScopes.NETWORK, {
         event: roomUseCaseLogEvents.JOIN_ROOM,
diff --git a/apps/server/src/network/types/connectionPorts.ts b/apps/server/src/network/types/connectionPorts.ts
index b025c7b..c96e091 100644
--- a/apps/server/src/network/types/connectionPorts.ts
+++ b/apps/server/src/network/types/connectionPorts.ts
@@ -35,7 +35,7 @@
 /** ゲームイベント調停で利用するルーム依存ポート */
 export type GameEventRoomUseCasePort = Pick<
   ConnectionRoomPort,
-  "getRoomByOwnerId" | "getRoomByPlayerId" | "markRoomPlaying" | "markRoomWaiting"
+  "getRoomByOwnerId" | "getRoomByPlayerId" | "markRoomPlaying" | "markRoomResult" | "markRoomWaiting"
 >;
 
 /** ゲームイベント調停で利用するランタイム依存ポート */
diff --git a/packages/shared/src/domains/room/room.type.ts b/packages/shared/src/domains/room/room.type.ts
index ce8c529..6fad7d7 100644
--- a/packages/shared/src/domains/room/room.type.ts
+++ b/packages/shared/src/domains/room/room.type.ts
@@ -31,7 +31,7 @@
 }
 
 /** ルーム参加拒否理由 */
-export type JoinRoomRejectedReason = "full" | "duplicate";
+export type JoinRoomRejectedReason = "full" | "duplicate" | "playing";
 
 /** ルーム参加拒否通知ペイロード */
 export interface JoinRoomRejectedPayload {
diff --git a/test/load-bot.constants.ts b/test/load-bot.constants.ts
index 48a406f..b8e9ad8 100644
--- a/test/load-bot.constants.ts
+++ b/test/load-bot.constants.ts
@@ -6,7 +6,7 @@
 
 export const URL = NETWORK_CONFIG.PROD_SERVER_URL;
 export const DEV_URL = NETWORK_CONFIG.DEV_SERVER_URL;
-export const BOTS = 10;
+export const BOTS = 99;
 export const DURATION_MS = Infinity;
 export const JOIN_DELAY_MS = 25;
 export const MOVE_TICK_MS = GAME_CONFIG.PLAYER_POSITION_UPDATE_MS;
@@ -19,7 +19,7 @@
 export const MAX_Y = GAME_CONFIG.GRID_ROWS;
 export const BOT_CAN_MOVE = true;
 export const BOT_CAN_PLACE_BOMB = true;
-export const ROOM_ID = "12";
+export const ROOM_ID = "1";
 export const START_GAME = true;
 export const SOCKET_PATH = NETWORK_CONFIG.SOCKET_IO_PATH;
 export const SOCKET_TRANSPORTS = [...NETWORK_CONFIG.SOCKET_TRANSPORTS];