Even if there is the ID verification confirmation of the ID signal that is transmitted in response to the request signal of the vehicle-inside transmitting antenna at the lock of the doors, the disablement of the ID code of the transmitter located inside the vehicle that has been registered at the memory is prohibited when at least one of operations of the lock switch of the transmitter that is located outside or inside the vehicle and the vehicle-inside switches is detected. Accordingly, the passenger inside the vehicle can start the engine by using the transmitter left behind in the vehicle.