To drive a piezoelectric transformer with higher efficiency by approximating the input voltage waveform and input current waveform of a piezoelectric transformer to the sine wave in order to reduce distortion and by selecting the frequency for higher efficiency.

Coils 23, 24 and capacitors 31, 32 attenuate the input current harmonic elements of the piezoelectric transformer and reduces a pulse current at the time of switching the transistors 41, 42 by connecting in series the transistor 41, coils 23, 21, 22, 24 and transistor 42, connecting an input power source to a connecting point of coils 21 and 22, connecting an input electrode 11 of the piezoelectric transformer 10 to a connecting point of the coils 23 and 21, connecting an input electrode 12 of the piezoelectric transformer 10 to a connecting point of the coils 22 and 24, connecting in parallel capacitors 31, 32 respectively to the transistors 41 and 42, driving transistors 41, 42 with a drive frequency control circuit 51, and magnetically coupling the coils 21, 22 and the coils 23 24.