An on-vehicle device has a receiving antenna for receiving a radio signal from a mobile device, a receiving circuit for returning an electric signal obtained by conversion by the receiving antenna to the original state, a control unit for determining whether a received signal from the receiving circuit is correct or incorrect, a driving circuit that is driven in response to a driving signal from the control unit and supplies antenna current to a vehicle antenna, and a detector for detecting whether the vehicle antenna operates normally. A detection signal of the detector is fed back to the control unit through the receiving circuit, and the failure determination of the vehicle antenna is performed.