diff --git a/apps/server/src/handlers/GameHandler.ts b/apps/server/src/handlers/GameHandler.ts
index 6477919..c26cf65 100644
--- a/apps/server/src/handlers/GameHandler.ts
+++ b/apps/server/src/handlers/GameHandler.ts
@@ -45,6 +45,14 @@
           x: updatedPlayer.x, 
           y: updatedPlayer.y 
         });
+
+        // ② 【新規】マス目の更新と差分送信のテスト
+        const cellUpdates = gameManager.paintAndGetUpdates(socket.id);
+        if (cellUpdates.length > 0) {
+          io.to(targetRoom).emit(SocketEvents.UPDATE_MAP_CELLS, cellUpdates);
+          // ログを出してサーバー側で送信されているか確認すると便利です
+          console.log(`[MAP_UPDATE] Sent ${cellUpdates.length} updates to room ${targetRoom}`);
+        }
       }
     }
   });
diff --git a/apps/server/src/managers/GameManager.ts b/apps/server/src/managers/GameManager.ts
index 73c7dd2..152cbe0 100644
--- a/apps/server/src/managers/GameManager.ts
+++ b/apps/server/src/managers/GameManager.ts
@@ -1,12 +1,17 @@
 import { Player } from "../entities/Player.js";
 import { GAME_CONFIG } from "@repo/shared/src/config/gameConfig";
+import { MapStore } from "../states/MapStore";
+import { getGridIndexFromPosition } from "@repo/shared/src/domains/gridMap/gridMap.logic";
+import type { CellUpdate } from "@repo/shared/src/domains/gridMap/gridMap.type";
 
 // プレイヤー集合の生成・更新・参照管理クラス
 export class GameManager {
   private players: Map<string, Player>;
+  private mapStore: MapStore;
 
   constructor() {
     this.players = new Map();
+    this.mapStore = new MapStore();
   }
 
   // 新規プレイヤー登録と初期位置設定処理
@@ -55,4 +60,17 @@
   getAllPlayers() {
     return Array.from(this.players.values());
   }
+
+  // 【一時的】移動したプレイヤーの足元を塗り、差分を返すメソッド
+  public paintAndGetUpdates(playerId: string): CellUpdate[] {
+    const player = this.players.get(playerId);
+    if (!player) return [];
+
+    const gridIndex = getGridIndexFromPosition(player.x, player.y);
+    if (gridIndex !== null) {
+      this.mapStore.paintCell(gridIndex, player.teamId);
+    }
+
+    return this.mapStore.getAndClearUpdates();
+  }
 }
\ No newline at end of file
diff --git a/apps/server/src/states/MapStore.ts b/apps/server/src/states/MapStore.ts
new file mode 100644
index 0000000..4f6f2be
--- /dev/null
+++ b/apps/server/src/states/MapStore.ts
@@ -0,0 +1,36 @@
+// apps/server/src/states/MapStore.ts
+import type { CellUpdate } from "@repo/shared/src/domains/gridMap/gridMap.type";
+import { GAME_CONFIG } from "@repo/shared/src/config/gameConfig";
+
+export class MapStore {
+  // 全マスの現在の色（teamId）を保持
+  private gridColors: number[];
+  // 次回の送信ループで送る差分リスト
+  private pendingUpdates: CellUpdate[];
+
+  constructor() {
+    // 初期状態は -1 (無色) などで初期化
+    const totalCells = GAME_CONFIG.GRID_COLS * GAME_CONFIG.GRID_ROWS;
+    this.gridColors = new Array(totalCells).fill(-1);
+    this.pendingUpdates = [];
+  }
+
+  /**
+   * マスを塗り、色が変化した場合のみ差分キューに追加する
+   */
+  public paintCell(index: number, teamId: number): void {
+    if (this.gridColors[index] !== teamId) {
+      this.gridColors[index] = teamId;
+      this.pendingUpdates.push({ index, teamId });
+    }
+  }
+
+  /**
+   * 溜まっている差分を取得し、キューをクリアする（ループ送信時に使用）
+   */
+  public getAndClearUpdates(): CellUpdate[] {
+    const updates = [...this.pendingUpdates];
+    this.pendingUpdates = [];
+    return updates;
+  }
+}
\ No newline at end of file