A diagnosis circuit 1 monitors a watchdog timer 2 and supplies a diagnosis result signal 1 indicating whether a monitoring result is normal or not to a diagnosis circuit 2. A diagnosis circuit 3 monitors a watchdog timer 1 and supplies a diagnosis result signal 3 indicating whether a monitoring result is normal or not to the diagnosis circuit 2. The diagnosis circuit 2 determines that the diagnosis circuit 1 or the watchdog timer 2 is abnormal when the diagnosis result signal 1 does not have a value indicating normal. Further, the diagnosis circuit 2 determines that the diagnosis circuit 3 or the watchdog timer 1 is abnormal when the diagnosis result signal 3 does not have a value indicating normal.