PURPOSE: To use one electrostatic vibrator both for transmitting and receiving operations by applying a wave transmitting drive signal to the primary winding of a transformer with one end of the secondary winding ground through two diodes connected to each other in reversed parallel while the vibrator is connected to the other end thereof through a clamp circuit.

CONSTITUTION: The outpt of a wave transmitting amplifier 1 is connected to the primary winding N1 of a boosting transformer 4 and diodes D1 and D2 connected to each other in reversed parallel are connected between one end of the secondary N2 and the ground. An electrostatic vibrator 2 is connected between the other end of the winding N2 and the ground through a clamp circuit 5 comprising a capacitor C2 and a diode D3. An input of a wave receiving amplifier 3 is connected at a connecting point between the winding N2 and the diodes D1 and D2 through a capacitor C1. The capacitor C2 of the circuit 5 is connected in series to the vibrator 2 and the diode D3 is connected in parallel to the vibrator 2 with an anode facing the ground. Thus, one electrostatic vibrator serves for wave receiving and transmitting operations concurrently.