diff --git a/src/main/java/info/istlab/IoTP/MqttWindow.java b/src/main/java/info/istlab/IoTP/MqttWindow.java
index f87a72a..44d871a 100644
--- a/src/main/java/info/istlab/IoTP/MqttWindow.java
+++ b/src/main/java/info/istlab/IoTP/MqttWindow.java
@@ -137,6 +137,7 @@
             appendToJTA("接続できませんでした。\n");
             jta.setBackground(Color.magenta);
             thread = null;
+            subscriber = null;
             return;
         }
         appendToJTA("Connected.\n");