To improve installing performance by providing an on-vehicle apparatus main body and a door opening/closing system on a vehicle, and incorporating a lock control means of the door opening/closing system into the on-vehicle apparatus main body.

In a door opening/closing system provided in relation to a radio main body 2 such as a car radio, for example, in the case where a door lock mean 14 is put in a lock condition, when an operation signal is transmitted from a transmitting antenna means 28 by operating a remote control means 20, a receiving antenna means 22 receives it. Next, an opening/closing system tuner means 24 encodes a received signal, and a lock control means 18 compares it with a prescribed code. In the case of a coincidence, an actuation signal is generated, and is sent and supplied to a lock actuating means 16, and a lock condition of the lock means 14 is released by actuating the actuating means 16. The tuner means 24 and the lock control means 18 are installed in the radio 2 as a lock opening/closing unit 30 so as to be mountable/demountable. Therefore, since a control part of the door opening/closing system is incorporated into the radio, it can be easily installed without requiring an exclusive space.