PURPOSE: To attain the continuous call of a question and an answer without effecting a transportation means for the receiving of an answer signal by making a power transportation signal and the answer signal from a responder into a transmission means by a different physical event.

CONSTITUTION: A question signal by a high frequency power signal to occur by a signal generator 1 is radiated in the air as an electromagnetic wave from an antenna 2 for transmission. A receiving antenna 2 to constitute a responder receives the supply of a high frequency power from the radiated electromagnetic wave as the question signal and a direct current output signal is generated as the output signal of a rectifying smoothing circuit 41. A question responding signal generator 42 generates the answer signal to the question as the signal on an amplitude axis or an signal on a time base with the output signal of the rectifying smoothing circuit 41 as a power source. The output signal of the sound wave signal generator generated electrically by the responder is converted to a sound and radiated in the air by an electric sound converter 5. Thus, with the signal generation of a frequency to meet the characteristic of the electric sound converter 5 as a purpose, for a sound wave generator 43, the sound radiated in the air is received by a sound electric converter 6 at the question side, converted to an electric answer signal and amplified with an amplifier 7. When the frequency generated by the sound wave generator 43 is a voice frequency, the output signal of the electric sound converter 5 can be heard with a voice.