PURPOSE: To make it easy to release a lock by providing a means to transmit call signals to a receiving terminal, a means to generate a control output in the case the call signals are received and a means to release the lock of a door.

CONSTITUTION: A command to transmit call signals to a receiving terminal equipment 6 placed in a private car 5 is transmitted from a radio transmitter 3 by dialing a telephone number designated in advance by using a nearby public telephone 2, etc. After that, antenna signals received through a receiving antenna 7 are detected by a receiving demodulation circuit 8 and are applied to a control circuit 9. Then, it is confirmed whether demodulating signals are the call signals or not in the circuit 9, and it is also confirmed whether it corresponds with a discrimination code stored in a memory 10 or not. It is applied to a door lock control circuit 13, and a door lock is released.