door opening closing signal to the input terminal sensing of the control unit 130 accordingly the control unit 130 determines the opened closed state of the door 20 according to the door opening closing signal received from the sensor unit 120 and determines whether the door switch 111 is turned on 200 as the result of the determination of operation 200 when the door switch 111 is turned on the control unit 130 determines that the door 20 is closed and outputs the door lock control signal to the door lock relay 140 through the output door_lock 202 in the door lock control signal as shown in fig3 the rectangular pulse is output for a predetermined time about 25 30 msec such that the door lock relay 140 operates in the pulsed mode and the time interval between pulses is gradually increased 1 sec 3 min 30 min according to the number of times of sensing of the contact of the door switch 111 to protect the door lock relay 140 accordingly in the door lock relay 140 the current flows in the control solenoid 142 for the predetermined time 25 to 30 msec according to the door lock control signal output from the output terminal door_lock of the control unit 130 and the common terminal com of the 3 pole switch 141 is switched from the normally closed terminal nc to the normally open terminal no 204 when the common terminal com of the 3 pole switch 141 is switched from the normally closed terminal nc to the normally open terminal no current of the power supply 100 flows to the main solenoid 113 of the door lock switch 110 through the common terminal com and the normally open terminal no of the 3 pole switch 141.