PURPOSE: To enable obtaining a high output in an always stable state by providing a monitor electrodes, which is shaped in the manner of tuning only through the abnormal oscillation of a rotor to output a voltage, between the sections of a piezoelectric element divided into two sections, by detecting the voltage generated from the monitor electrode, and by controlling a driving signal applied to the piezoelectric element to drive the rotor.

CONSTITUTION: A piezoelectric element 2 divided into two sections is stuck to a ring-shaped stator 1 and a monitor electrode 3 is provided between these sections. Desirably, the monitor electrode 3 is shaped in the manner of generating voltage not by a fundamental frequency but at the time of getting too near a resonance frequency. When the driving frequency of an ultrasonic motor gets near the resonance frequency and an abnormal sound by the abnormal oscillation of a rotor is generated, voltage is outputted from the monitor electrode 3 and the signal of an oscillator 9 is set according to the detected value of the voltage and a driving signal for driving the motor is controlled suitably. Thus, the ultrasonic motor can be driven at the driving frequency near to the resonance frequency to enable rotating with a high output and preventing an abnormal sound generated for a long time.