To increase satisfactory operation of a circuit and the durability of a positive-characteristic thermistor.

A resistor RO is connected to a relay coil RC in parallel. Relay coil applied voltage ER is separated from resistor applied voltage, therefore, the time at which the relay coil applied voltage ER is reduced more than holding voltage EO is shortened more than in a conventional circuit. Two Zener diodes whose forward directions face each other are connected to the motor M side of a relay contact RS and the capacitor C side of the relay coil RC. The relay coil applied voltage ER is equal to [Applied voltage EM to motor -(Zener diode forward-directional drop voltage + Zener voltage)], therefore, the time at which the relay coil applied voltage ER is reduced more than the holding voltage EO is shortened more than in the conventional circuit. The time from the lock of the motor M to turning off the relay contact RS can be shortened, therefore the time at which the lock current flows through the positive characteristic thermistor PTC is shortened, thus it is possible to eliminate the operational fault of the circuit, thereby enhancing the durability of the positive-characteristics thermistor PTC.