PURPOSE: To improve the power efficiency of a piezoelectric element, by providing a converter controller for making ON/OFF control of a first switching element until the voltage between terminals reaches to a predetermined level when the piezoelectric element is charged, and for making ON/OFF control of a second switching element when the piezoelectric element is discharged.

CONSTITUTION: Output V2 from an AND gate 81 is same as the output from a rectangular wave oscillator 80 only during the interval where a drive signal V1 is high, and it is low during other interval. Output V3 from a comparator 70 is high until time (t2) when the terminal voltage -E2 of a piezoelectric element 2 exceeds over a referential voltage Et in the negative direction, and the output V4 has an inverted waveform of the output V2. Consequently, a transistor 31 is turned OFF and keeps the OFF state until time (t1) and turned ON/OFF repeatedly during the times (t1)W(t2), then turned OFF at time passing the (t2). At time (t3), the output V5 goes high and keeps high until time (t4), and the output V6 has the same waveform as the output from the rectangular wave oscillator 80. Consequently, the base voltage of a transistor 32 is brought to the ground potential while vibrating, and it is turned ON/OFF, thereby charges in the piezoelectric element 2 are regenerated by a DC power source 1 through the counter electromotive force produced in a coil 50.