PURPOSE: To prevent a mechanical oscillation in a bimorph by shaping a saw tooth wave deflecting voltage so that it has a gentle amplitude characteristic in the period when the amplitude characteristic of the deflecting voltage is changed rapidly.

CONSTITUTION: Integral characteristics 6 and 7 are changed in accordance with the frequency of the control pulse from a control pulse generator 5, and integrators integrate hardly a voltage when the control pulse is ≥300kHz. A switching pulse (a) or (b) is inputted to a terminal 10. Monostable multivibrators 15 and 16 output pulses (i) and (j) corresponding to periods when the amplitude of the saw tooth wave deflecting voltage is changed rapidly. The control pulse generator 5 outputs control pulses (a) and (b) having frequencies 1kHz and 500kHz from terminals A and B. Both pulses are selected alternately by switches 31 and 34 and are given to the integrator 6. They are given to the integrator 7 also similarly. Consequently, saw tooth deflecting voltage (d) and (c) are integrated in periods of pulses (i) and (j) by said characteristics of integrators, and integral outputs (m) and (k) are taken out from integrators. An error output from a tracking control circuit 4 is superposed onto integral outputs (m) and (k), and they are given to a pair of bimorph plates.