iPhone app showing Rotation button in iPad

We created iPhone app for portrait mode only. App is running fine in iPhone. but when we run the same app in iPad some time we are getting rotation button along with scale button. Rotation button is rotating app in landscape and our app is not support so UI is look bad. We want to disable rotation button forever. We search for setting which can be used enable/disable this rotation button but did not found. Check attached screen shot for reference.