To constitute a responder simply and at low costs and to transmit data for response to an interrogator at high quality.

Carrier waves 30a in which a prescribed-cycle signal is modulated by microwaves are transmitted from an interrogator 1. The carrier waves 30a are received by a reception part 22 in a responder 2. In a high-frequency- wave generation part 25, high-frequency waves which are used to transmit data for response to the interrogator 1 are generated from the prescribed-cycle signal contained in the carrier waves 30a, thereby synchronize the high-frequency waves with the operation of a control part 21 in the interrogator 1. Thus, the constitution of every circuit in the interrogator 1 which receives carrier waves 30b modulated by the generated high-frequency waves can make synchronous capture easy.