PURPOSE: To miniaturize the equipment and to eliminate the need for the provision of a power supply such as a battery by applying electromagnetic coupling between a coil of a resonance circuit at the transmission side and a coil of an oscillation circuit at the reception side and providing a coil for power supply.

CONSTITUTION: When coils L01, L02 are subject to induction coupling, a voltage is induced in the coil L02. The voltage is inputted to a rectifier smoothing circuit 33, where the voltage is smoothed and fed to a switching element 21 and a control circuit 22 as the operating voltage. Thus, the control circuit 22 reads a data in a memory to turn on/off the switching element 21 based on the data. The on/off state is detected by an FM demodulation circuit 13 via the coil L2 of the resonance circuit 2 and the coil L1 of the resonance circuit 1 and received as information.