When a clutch relay connects between a control device and a vehicle electric power source in response to outputting of a clutch OFF signal from an electronic control device to the clutch relay, a timer circuit starts a control operation for energizing coil portions. When a predetermined time period elapses, the timer circuit terminates energization of the coil portions. When the clutch relay connects between the control device and the vehicle electric power source in response to outputting of a clutch ON signal from the electronic control device to the relay, the timer circuit starts a control operation for energizing the coil portions. When a predetermined time period elapses, the timer circuit terminates energization of the coil portions.