diff --git a/apps/client/src/hooks/useAppFlow.ts b/apps/client/src/hooks/useAppFlow.ts
index 2bcc332..ed9d840 100644
--- a/apps/client/src/hooks/useAppFlow.ts
+++ b/apps/client/src/hooks/useAppFlow.ts
@@ -30,6 +30,10 @@
   };
 
   const requestJoin = (payload: roomTypes.JoinRoomPayload) => {
+    if (isJoining) {
+      return;
+    }
+
     clearJoinTimeout();
     setJoinErrorMessage(null);
     setIsJoining(true);
diff --git a/apps/server/src/network/handlers/room/registerRoomHandlers.ts b/apps/server/src/network/handlers/room/registerRoomHandlers.ts
index 7d7fbbf..dcb5b46 100644
--- a/apps/server/src/network/handlers/room/registerRoomHandlers.ts
+++ b/apps/server/src/network/handlers/room/registerRoomHandlers.ts
@@ -44,32 +44,37 @@
     });
 
     // 参加拒否時は理由を通知する
-    if (joinResult.status === "full") {
-      socket.leave(roomId);
-      roomPublisher.publishJoinRejected({
-        roomId,
-        reason: "full",
-      });
-      logEvent("Network", {
-        event: "JOIN_ROOM",
-        result: "rejected_room_full",
-        roomId,
-        socketId: socket.id,
-      });
-      return;
-    }
+    switch (joinResult.status) {
+      case "full":
+        socket.leave(roomId);
+        roomPublisher.publishJoinRejected({
+          roomId,
+          reason: "full",
+        });
+        logEvent("Network", {
+          event: "JOIN_ROOM",
+          result: "rejected_room_full",
+          roomId,
+          socketId: socket.id,
+        });
+        return;
 
-    if (joinResult.status === "duplicate") {
-      roomPublisher.publishJoinRejected({
-        roomId,
-        reason: "duplicate",
-      });
-      logEvent("Network", {
-        event: "JOIN_ROOM",
-        result: "rejected_duplicate",
-        roomId,
-        socketId: socket.id,
-      });
+      case "duplicate":
+        roomPublisher.publishJoinRejected({
+          roomId,
+          reason: "duplicate",
+        });
+        logEvent("Network", {
+          event: "JOIN_ROOM",
+          result: "rejected_duplicate",
+          roomId,
+          socketId: socket.id,
+        });
+        return;
+
+      case "joined":
+      default:
+        return;
     }
   });
 };