PURPOSE: To stably rotate an ultrasonic motor with high efficiency and performance by detecting the amplitude of a feedback voltage, and detecting the phase difference between the feedback voltage and an exciting frequency voltage.

CONSTITUTION: A driving circuit for an ultrasonic motor oscillates a sawtooth wave having frequency (f) four times the frequency for exciting a stator by an oscillator 1, and outputs it to a distributor 3. The distributor 3 divides the input sawtooth wave into four 1-4, and outputs them as time-shifted rectangular waves. The outputs 1-4 are input to an output transformer 4 through an amplifier 4 of next stage. When the inductance components of its secondary side and the intrinsic electrostatic capacity component of an electromechanical conversion vibrator satisfy a resonance condition, quasi-sine wave and quasi- cosine wave are applied as outputs to the electrodes 7a, 7b of the stator 7 of a motor. An amplitude, phase control signals are generated by the feedback voltage obtained by an electrode 7c.