A transmitter of an on-vehicle device transmits a request signal from a first antenna, and transmits first measurement signals at different timings from the first antenna and a second antenna. The receiver receives a first response signal including information on transmission intensities of a second measurement signals to be transmitted from the first and second antennas. The transmitter further transmits the second measurement signals at different timings from the first and second antennas. The second measurement signals have transmission intensities respectively set based on the information on transmission intensities included in the first response signal. The receiver receives a second response signal transmitted when a relationship between the reception intensities of the second measurement signals transmitted from the first and second antennas agrees with the information on the transmission intensities included in the first response signal.