PURPOSE: To rapidly reduce residual charge by bringing the voltage between both terminals of a piezoelectric element by regenerating the charge of the piezoelectric element to a power supply at the predetermined point of time of the resonance cycle of a resonance circuit and discharging the charge of the piezoelectric element from the intermediate tap of a coil through a transistor.

CONSTITUTION: The first switch means 1 consisting of the coil L in series to a piezoelectric element 2, transistors Tr1, Tr2, resistors R4, R5 and a diode D4 and supplying exciting voltage Eo to the aforementioned coil L and a means (diode 5) regenerating the charge of the piezoelectric element 2 to a power supply when the first switching means 1 is turned OFF are provided in parallel. Further, the second switch means equipped with the transistor Tr3 connected to the intermediate tap M of the coil L and turned ON by predetermined coil voltage and discharging the charge of the piezoelectric element 2 is connected. By this constitution, a part of the charge of the piezoelectric element 2 is regenerated to the power supply and a part thereof is discharged through a discharge circuit.