In a mobile body discrimination apparatus having an interrogator apparatus and a plurality of transponders each capable of transmitting information to the interrogator apparatus by modulation of radio waves that are reflected from a transponder antenna, which can be attached to respective articles, store data concerning the articles, and transmit the data to the interrogator apparatus in response to a command signal transmitted while the transponder traverses a communication region of an antenna of the interrogator apparatus, each transponder is configured to begin sending such response data after a randomly determined time interval following reception of the command signal, thereby reducing the probability of data conflict when plural transponders are within the communication region. In addition, radio waves from a second antenna of the interrogator apparatus are directed into that communication region in the intervals between transmissions of the command signal, thereby increasing the power level of radio waves that are reflected by a transponder antenna or used by a rectifier circuit to supply power for operating the transponder circuits.