PURPOSE: To stabilize output of piezoelectric element by compensating fat temperature drift thereof through a simple method without requiring measurement of displacement of piezoelectric element or output feedback thereof.

CONSTITUTION: A temperature-sensing element 3 detects temperature of a piezoelectric element 2. A voltage signal modulation circuit 6A varies the level of an AC voltage signal V1 depending on the temperature thus detected. Output from the modulation circuit 6 is passed through a half-wave rectifying circuit 9a and an adder circuit 18 and superposed on a DC voltage signal V1 and then it is applied on the piezoelectric element 2 thus causing self-heating thereof. Output from the modulation circuit 6A is also passed through a rectifying/ smoothing circuit 8 and an adder circuit 18 where it is superposed on a DC voltage command signal V1 and then applied on the piezoelectric element 2 in order to correct displacement thereof. In this regard, the modulation circuit 6A controls the output thereof through two correcting functions such that fluctuation in the displacement of the piezoelectric element 2 due to temperature is suppressed.