diff --git a/.idea/deploymentTargetSelector.xml b/.idea/deploymentTargetSelector.xml
index b268ef3..49d03f9 100644
--- a/.idea/deploymentTargetSelector.xml
+++ b/.idea/deploymentTargetSelector.xml
@@ -4,6 +4,14 @@
     <selectionStates>
       <SelectionState runConfigName="app">
         <option name="selectionMode" value="DROPDOWN" />
+        <DropdownSelection timestamp="2025-12-16T05:02:35.747299Z">
+          <Target type="DEFAULT_BOOT">
+            <handle>
+              <DeviceId pluginId="LocalEmulator" identifier="path=C:\Users\natsu\.android\avd\Pixel_7_2.avd" />
+            </handle>
+          </Target>
+        </DropdownSelection>
+        <DialogSelection />
       </SelectionState>
     </selectionStates>
   </component>
diff --git a/.idea/gradle.xml b/.idea/gradle.xml
index 0897082..639c779 100644
--- a/.idea/gradle.xml
+++ b/.idea/gradle.xml
@@ -4,6 +4,7 @@
   <component name="GradleSettings">
     <option name="linkedExternalProjectsSettings">
       <GradleProjectSettings>
+        <option name="testRunner" value="CHOOSE_PER_TEST" />
         <option name="externalProjectPath" value="$PROJECT_DIR$" />
         <option name="gradleJvm" value="#GRADLE_LOCAL_JAVA_HOME" />
         <option name="modules">
@@ -12,7 +13,6 @@
             <option value="$PROJECT_DIR$/app" />
           </set>
         </option>
-        <option name="resolveExternalAnnotations" value="false" />
       </GradleProjectSettings>
     </option>
   </component>
diff --git a/app/src/main/java/com/example/tampopo_client/views/FriendIconView.java b/app/src/main/java/com/example/tampopo_client/views/FriendIconView.java
index e4c197e..4b4bba9 100644
--- a/app/src/main/java/com/example/tampopo_client/views/FriendIconView.java
+++ b/app/src/main/java/com/example/tampopo_client/views/FriendIconView.java
@@ -33,6 +33,7 @@
     private String friendUserId;
     private String friendUserNickname;
     private ChatViewModel chatViewModel;
+    private boolean isActivityObserverRegistered = false;
 
     //ActivityLiveData
     private final Observer<List<Activity>> activitiesObserver = new Observer<List<Activity>>() {
@@ -64,6 +65,14 @@
         return chatObserver;
     }
 
+    public boolean isActivityObserverRegistered() {
+        return isActivityObserverRegistered;
+    }
+
+    public void setActivityObserverRegistered(boolean registered) {
+        isActivityObserverRegistered = registered;
+    }
+
     public FriendIconView(Context context, String friendUserId, String friendUserNickname, ChatViewModel chatViewModel) {
         this(context);
         this.friendUserId = friendUserId;
diff --git a/app/src/main/java/com/example/tampopo_client/views/MainActivity.java b/app/src/main/java/com/example/tampopo_client/views/MainActivity.java
index f6b4111..7211ab7 100644
--- a/app/src/main/java/com/example/tampopo_client/views/MainActivity.java
+++ b/app/src/main/java/com/example/tampopo_client/views/MainActivity.java
@@ -350,9 +350,12 @@
                 userViews.put(friendId, container);
                 userView = container;
                 //messageList.addView(container);
+            }
 
-                // TODO: CHANGE
-                activitiesLiveData.observeForever(container.getActivitiesObserver());
+            // Observerがまだ登録されていない場合は登録する
+            if (!userView.isActivityObserverRegistered()) {
+                activitiesLiveData.observeForever(userView.getActivitiesObserver());
+                userView.setActivityObserverRegistered(true);
             }
 
             ConstraintSet set = new ConstraintSet();