diff --git a/apps/client/src/scenes/game/entities/map/GameMapView.ts b/apps/client/src/scenes/game/entities/map/GameMapView.ts
index 5c5185b..c065a25 100644
--- a/apps/client/src/scenes/game/entities/map/GameMapView.ts
+++ b/apps/client/src/scenes/game/entities/map/GameMapView.ts
@@ -98,8 +98,9 @@
 
   /** チームIDから塗り色の16進数カラー値を取得する */
   private toHexColor(teamId: number): number {
+    config.assertValidTeamId(teamId);
     const { TEAM_COLORS } = config.GAME_CONFIG;
-    const colorString = TEAM_COLORS[teamId] || '#FFFFFF';
+    const colorString = TEAM_COLORS[teamId];
     return parseInt(colorString.replace('#', '0x'), 16);
   }
 }
\ No newline at end of file
diff --git a/apps/client/src/scenes/game/entities/player/PlayerView.ts b/apps/client/src/scenes/game/entities/player/PlayerView.ts
index fed76a3..2717ebd 100644
--- a/apps/client/src/scenes/game/entities/player/PlayerView.ts
+++ b/apps/client/src/scenes/game/entities/player/PlayerView.ts
@@ -10,7 +10,7 @@
   public readonly displayObject: Sprite;
 
   constructor(teamId: number, isLocal: boolean) {
-    const { PLAYER_RADIUS_PX } = config.GAME_CONFIG;
+    const { PLAYER_RADIUS_PX, TEAM_COUNT } = config.GAME_CONFIG;
 
     // 🌟 1. チームIDと画像ファイル名の紐づけ（すべて .svg に変更しました！）
     const characterImages = [
@@ -20,8 +20,16 @@
       "/yellow.svg", // teamId: 3 のときの画像
     ];
 
+    if (characterImages.length !== TEAM_COUNT) {
+      throw new Error(
+        `GAME_CONFIG mismatch: characterImages length (${characterImages.length}) must equal TEAM_COUNT (${TEAM_COUNT})`,
+      );
+    }
+
+    config.assertValidTeamId(teamId);
+
     // 配列から対応する画像ファイル名を取得（デフォルトは red.svg）
-    const imageFileName = (characterImages[teamId] || "/red.svg").replace(
+    const imageFileName = characterImages[teamId].replace(
       /^\//,
       "",
     );
diff --git a/apps/server/src/domains/game/application/services/TeamAssignmentService.ts b/apps/server/src/domains/game/application/services/TeamAssignmentService.ts
index 4ee8c50..fe9c33b 100644
--- a/apps/server/src/domains/game/application/services/TeamAssignmentService.ts
+++ b/apps/server/src/domains/game/application/services/TeamAssignmentService.ts
@@ -10,10 +10,8 @@
    * 現在のプレイヤー状況から、最も人数が少ないチームIDを算出する
    */
   public static getBalancedTeamId(currentPlayers: Map<string, Player>): number {
+    config.validateTeamConfig();
     const teamCount = config.GAME_CONFIG.TEAM_COUNT;
-    if (config.GAME_CONFIG.TEAM_COLORS.length !== teamCount) {
-      throw new Error("GAME_CONFIG mismatch: TEAM_COLORS length must equal TEAM_COUNT");
-    }
     const teamPopulations = new Array(teamCount).fill(0);
 
     // 現在の各チームの所属人数を数え上げる
diff --git a/packages/shared/src/config/gameConfig.ts b/packages/shared/src/config/gameConfig.ts
index b072e01..51ca802 100644
--- a/packages/shared/src/config/gameConfig.ts
+++ b/packages/shared/src/config/gameConfig.ts
@@ -60,4 +60,24 @@
   MAP_BG_COLOR: 0x111111,     // 何も塗っていないマス（背景）の色
   MAP_GRID_COLOR: 0x333333,   // グリッド線の色
   MAP_BORDER_COLOR: 0xff4444, // プレイ領域外枠の色
-} as const;
\ No newline at end of file
+} as const;
+
+/** TEAM_COUNT と TEAM_COLORS の整合性を検証する */
+export const validateTeamConfig = (): void => {
+  const { TEAM_COUNT, TEAM_COLORS } = GAME_CONFIG;
+  if (TEAM_COLORS.length !== TEAM_COUNT) {
+    throw new Error(
+      `GAME_CONFIG mismatch: TEAM_COLORS length (${TEAM_COLORS.length}) must equal TEAM_COUNT (${TEAM_COUNT})`,
+    );
+  }
+};
+
+/** teamId が有効範囲内かを検証する */
+export const assertValidTeamId = (teamId: number): void => {
+  validateTeamConfig();
+
+  const { TEAM_COUNT } = GAME_CONFIG;
+  if (!Number.isInteger(teamId) || teamId < 0 || teamId >= TEAM_COUNT) {
+    throw new Error(`Invalid teamId: ${teamId}`);
+  }
+};
\ No newline at end of file
diff --git a/packages/shared/src/config/index.ts b/packages/shared/src/config/index.ts
index 75f5253..e34af47 100644
--- a/packages/shared/src/config/index.ts
+++ b/packages/shared/src/config/index.ts
@@ -1,2 +1,3 @@
 export { GAME_CONFIG } from "./gameConfig";
+export { validateTeamConfig, assertValidTeamId } from "./gameConfig";
 export { NETWORK_CONFIG } from "./networkConfig";