PURPOSE: To make a device compact and light in weight by sharing the same semiconductor element both for a detection circuit to detect transmitted signals from a base unit and for a modulation circuit for transmission from an ID tag concerning the transmitter/receiver utilized for the ID tag or the like so as to transmit previously determined proper information to the base unit in response to a call from the base unit, for example.

CONSTITUTION: An amplitude modulated signal, for which a carrier wave is modulated in amplitude with a prescribed signal, is impressed to a detection circuit 13 composed of the non-linear semiconductor element which voltage/ current characteristic is non-linear, a pulse train from a modulated pulse train generator 15 is impressed to the non-linear semiconductor element, either of the bias or the impedance is changed with a previously decided pattern at least, and the detected output of the detection circuit 13 to be changed along with the change is transmitted from an antenna 16.