PURPOSE: To transmit and receive a stable wide-band output with small-sized constitution by using a low-voltage power source by supplying a high-voltage transmitted signal to an oscillator by boosting a transmitted voltage during transmission, and outputting the received voltage from input and output terminals common to the transmission.

CONSTITUTION: On the same core, primary and secondary coils L1 and L2 are provided, oscillators E1∼E9 are connected, and diodes CR1∼CR4 are further arranged. For the operation of a transmitter, the diodes CR1 and CR2 short-circuit because they are cut-off diodes having lower levels than a transmitted signal, so that the transmitted signal is applied to both the terminals of the coil L1. Those coils L1 and L2 are wound around the same core, the transmitted signal obtained by boosting a high voltage is supplied to the oscillators E1∼E9. For the operation of a receiver, on the other hand, the diodes CR1∼CR4 never conduct because the received voltages of the oscillators E1∼E9 are very low, so the received voltage is developed between terminals 1 and 2 through the coil L2.