diff --git a/apps/server/src/domains/game/GameHandler.ts b/apps/server/src/domains/game/GameHandler.ts
index 46f5057..d1409db 100644
--- a/apps/server/src/domains/game/GameHandler.ts
+++ b/apps/server/src/domains/game/GameHandler.ts
@@ -1,99 +1,34 @@
 import { Server, Socket } from "socket.io";
 import { GameManager } from "./GameManager";
 import { RoomManager } from "@server/domains/room/RoomManager";
-import { protocol, roomConsts } from "@repo/shared";
+import { protocol } from "@repo/shared";
 import type { playerTypes } from "@repo/shared";
+import { onPing } from "./handlers/onPing";
+import { onStartGame } from "./handlers/onStartGame";
+import { onReadyForGame } from "./handlers/onReadyForGame";
+import { onMove } from "./handlers/onMove";
+import { onDisconnect } from "./handlers/onDisconnect";
 
 export const registerGameHandlers = (io: Server, socket: Socket, gameManager: GameManager, roomManager: RoomManager) => {
   
   // クライアントから送られてきた時刻をそのまま返しつつ、サーバーの現在時刻も添える
   socket.on(protocol.SocketEvents.PING, (clientTime: number) => {
-    socket.emit(protocol.SocketEvents.PONG, { clientTime, serverTime: Date.now() });
+    onPing(socket, clientTime);
   });
 
   // ゲーム開始要求処理
   socket.on(protocol.SocketEvents.START_GAME, () => {
-    const room = roomManager.getRoomByOwnerId(socket.id);
-    if (!room) {
-      console.log("[GameHandler] START_GAME ignored (no room)", { socketId: socket.id });
-      return;
-    }
-
-    if (room.status === roomConsts.RoomPhase.PLAYING) {
-      console.log("[GameHandler] START_GAME ignored (already playing)", { roomId: room.roomId });
-      return;
-    }
-
-    console.log("[GameHandler] START_GAME accepted", {
-      roomId: room.roomId,
-      ownerId: socket.id,
-      totalPlayers: room.players.length
-    });
-
-    if (room) {
-      room.status = roomConsts.RoomPhase.PLAYING;
-
-      const playerIds = room.players.map((p: { id: string }) => p.id);
-      
-      // 同ルーム全プレイヤーのゲーム管理登録
-      room.players.forEach((p: { id: string }) => {
-        gameManager.addPlayer(p.id);
-      });
-
-      // 20Hzのゲームループを開始し、毎フレームの送信処理を定義
-      gameManager.startGameLoop(
-        room.roomId, 
-        playerIds, 
-        (tickData) => {
-        // 1. 各プレイヤーの最新座標をクライアントに送信
-        tickData.players.forEach((playerData) => {
-          io.to(room.roomId).emit(protocol.SocketEvents.UPDATE_PLAYER, playerData);
-        });
-
-        // 2. 差分があれば、ルーム内の全員に一斉送信
-        if (tickData.cellUpdates.length > 0) {
-          io.to(room.roomId).emit(protocol.SocketEvents.UPDATE_MAP_CELLS, tickData.cellUpdates);
-        }
-      },
-
-      () => {
-          // 3分経過時に GameLoop から呼ばれる処理
-          console.log(`[GameHandler] ルーム ${room.roomId} のゲームが終了しました (3分経過)`);
-          io.to(room.roomId).emit(protocol.SocketEvents.GAME_END); // クライアントへ終了通知
-          room.status = roomConsts.RoomPhase.WAITING; // ルーム状態を待機に戻す
-        }
-      );
-        
-      // GameManagerから開始時刻を取得し、GAME_STARTイベントにデータを乗せて送る
-      const startTime = gameManager.getRoomStartTime(room.roomId) || Date.now();
-      io.to(room.roomId).emit(protocol.SocketEvents.GAME_START, { startTime });
-    }
+    onStartGame(io, gameManager, roomManager, socket.id);
   });
 
   // 画面準備完了通知受信時初期データ返却
   socket.on(protocol.SocketEvents.READY_FOR_GAME, () => {
-    const allPlayers = gameManager.getAllPlayers();
-    socket.emit(protocol.SocketEvents.CURRENT_PLAYERS, allPlayers);
-    console.log("[GameHandler] READY_FOR_GAME received", { socketId: socket.id, totalPlayers: allPlayers.length });
-
-    // 準備が完了したクライアントに対して、改めて開始時刻を個別に教える
-    // Socket.ioの仕様上、socket.roomsには自身のIDと参加中のルームIDが含まれるため、そこからルームIDを特定する
-    const roomId = Array.from(socket.rooms).find(room => room !== socket.id);
-    if (roomId) {
-      const startTime = gameManager.getRoomStartTime(roomId);
-      if (startTime) {
-        // io.to() による全員への一斉送信ではなく、socket.emit() でこの本人にだけ送る
-        socket.emit(protocol.SocketEvents.GAME_START, { startTime });
-        console.log("[GameHandler] GAME_START sent to ready client", { socketId: socket.id, roomId, startTime });
-      }
-    } else {
-      console.log("[GameHandler] READY_FOR_GAME missing roomId", { socketId: socket.id });
-    }
+    onReadyForGame(socket, gameManager);
   });
 
   // ゲームプレイ中イベント群
   socket.on(protocol.SocketEvents.MOVE, (data: playerTypes.MovePayload) => {
-    gameManager.movePlayer(socket.id, data.x, data.y);
+    onMove(gameManager, socket.id, data);
   });
 
 };
@@ -102,9 +37,5 @@
  * 切断時のゲームクリーンアップ処理
  */
 export const handleGameDisconnect = (io: Server, gameManager: GameManager, playerId: string) => {
-  // ゲームからの除外処理
-  gameManager.removePlayer(playerId);
-  // 全体にプレイヤー削除を通知
-  io.emit(protocol.SocketEvents.REMOVE_PLAYER, playerId);
-  console.log("[GameHandler] player removed", { playerId });
+  onDisconnect(io, gameManager, playerId);
 };
\ No newline at end of file
diff --git a/apps/server/src/domains/game/handlers/onDisconnect.ts b/apps/server/src/domains/game/handlers/onDisconnect.ts
new file mode 100644
index 0000000..4cc4b5f
--- /dev/null
+++ b/apps/server/src/domains/game/handlers/onDisconnect.ts
@@ -0,0 +1,13 @@
+import { Server } from "socket.io";
+import { GameManager } from "@server/domains/game/GameManager";
+import { protocol } from "@repo/shared";
+
+export const onDisconnect = (
+  io: Server,
+  gameManager: GameManager,
+  playerId: string
+) => {
+  gameManager.removePlayer(playerId);
+  io.emit(protocol.SocketEvents.REMOVE_PLAYER, playerId);
+  console.log("[GameHandler] player removed", { playerId });
+};
diff --git a/apps/server/src/domains/game/handlers/onMove.ts b/apps/server/src/domains/game/handlers/onMove.ts
new file mode 100644
index 0000000..7288ce3
--- /dev/null
+++ b/apps/server/src/domains/game/handlers/onMove.ts
@@ -0,0 +1,10 @@
+import { GameManager } from "@server/domains/game/GameManager";
+import type { playerTypes } from "@repo/shared";
+
+export const onMove = (
+  gameManager: GameManager,
+  playerId: string,
+  data: playerTypes.MovePayload
+) => {
+  gameManager.movePlayer(playerId, data.x, data.y);
+};
diff --git a/apps/server/src/domains/game/handlers/onPing.ts b/apps/server/src/domains/game/handlers/onPing.ts
new file mode 100644
index 0000000..2045d39
--- /dev/null
+++ b/apps/server/src/domains/game/handlers/onPing.ts
@@ -0,0 +1,6 @@
+import { Socket } from "socket.io";
+import { protocol } from "@repo/shared";
+
+export const onPing = (socket: Socket, clientTime: number) => {
+  socket.emit(protocol.SocketEvents.PONG, { clientTime, serverTime: Date.now() });
+};
diff --git a/apps/server/src/domains/game/handlers/onReadyForGame.ts b/apps/server/src/domains/game/handlers/onReadyForGame.ts
new file mode 100644
index 0000000..f7c845b
--- /dev/null
+++ b/apps/server/src/domains/game/handlers/onReadyForGame.ts
@@ -0,0 +1,30 @@
+import { Socket } from "socket.io";
+import { GameManager } from "@server/domains/game/GameManager";
+import { protocol } from "@repo/shared";
+
+export const onReadyForGame = (
+  socket: Socket,
+  gameManager: GameManager
+) => {
+  const allPlayers = gameManager.getAllPlayers();
+  socket.emit(protocol.SocketEvents.CURRENT_PLAYERS, allPlayers);
+  console.log("[GameHandler] READY_FOR_GAME received", {
+    socketId: socket.id,
+    totalPlayers: allPlayers.length,
+  });
+
+  const roomId = Array.from(socket.rooms).find((room) => room !== socket.id);
+  if (roomId) {
+    const startTime = gameManager.getRoomStartTime(roomId);
+    if (startTime) {
+      socket.emit(protocol.SocketEvents.GAME_START, { startTime });
+      console.log("[GameHandler] GAME_START sent to ready client", {
+        socketId: socket.id,
+        roomId,
+        startTime,
+      });
+    }
+  } else {
+    console.log("[GameHandler] READY_FOR_GAME missing roomId", { socketId: socket.id });
+  }
+};
diff --git a/apps/server/src/domains/game/handlers/onStartGame.ts b/apps/server/src/domains/game/handlers/onStartGame.ts
new file mode 100644
index 0000000..e27d612
--- /dev/null
+++ b/apps/server/src/domains/game/handlers/onStartGame.ts
@@ -0,0 +1,58 @@
+import { Server } from "socket.io";
+import { GameManager } from "@server/domains/game/GameManager";
+import { RoomManager } from "@server/domains/room/RoomManager";
+import { protocol, roomConsts } from "@repo/shared";
+
+export const onStartGame = (
+  io: Server,
+  gameManager: GameManager,
+  roomManager: RoomManager,
+  ownerId: string
+) => {
+  const room = roomManager.getRoomByOwnerId(ownerId);
+  if (!room) {
+    console.log("[GameHandler] START_GAME ignored (no room)", { socketId: ownerId });
+    return;
+  }
+
+  if (room.status === roomConsts.RoomPhase.PLAYING) {
+    console.log("[GameHandler] START_GAME ignored (already playing)", { roomId: room.roomId });
+    return;
+  }
+
+  console.log("[GameHandler] START_GAME accepted", {
+    roomId: room.roomId,
+    ownerId,
+    totalPlayers: room.players.length,
+  });
+
+  room.status = roomConsts.RoomPhase.PLAYING;
+
+  const playerIds = room.players.map((p: { id: string }) => p.id);
+
+  room.players.forEach((p: { id: string }) => {
+    gameManager.addPlayer(p.id);
+  });
+
+  gameManager.startGameLoop(
+    room.roomId,
+    playerIds,
+    (tickData) => {
+      tickData.players.forEach((playerData) => {
+        io.to(room.roomId).emit(protocol.SocketEvents.UPDATE_PLAYER, playerData);
+      });
+
+      if (tickData.cellUpdates.length > 0) {
+        io.to(room.roomId).emit(protocol.SocketEvents.UPDATE_MAP_CELLS, tickData.cellUpdates);
+      }
+    },
+    () => {
+      console.log(`[GameHandler] ルーム ${room.roomId} のゲームが終了しました (3分経過)`);
+      io.to(room.roomId).emit(protocol.SocketEvents.GAME_END);
+      room.status = roomConsts.RoomPhase.WAITING;
+    }
+  );
+
+  const startTime = gameManager.getRoomStartTime(room.roomId) || Date.now();
+  io.to(room.roomId).emit(protocol.SocketEvents.GAME_START, { startTime });
+};