An on-vehicle control unit includes a memory storing a first data group having signal strength information of a plurality of request signals transmitted from a plurality of transmitting antennas before and after movement of a movable object when a portable device is placed along an inner surface of a vehicle and a second data group having signal strength information of the plurality of request signals transmitted from the plurality of transmitting antennas before and after the movement of the movable object when the portable device is placed along an outer surface of the vehicle. The on-vehicle control unit determines which of the first and second data groups request signal strength information received from the portable device closely resembles.