PURPOSE: To make step driving easy of sequential control possible by making a plurality of projections on the rotor of an ultrasonic motor and bringing the projections into contact with a stator.
CONSTITUTION: A wave step motor has piezoelectric elements 3 used as vibrators and a stator 2 fastened to a bottom board 4 with a screw 6. A rotor 1 is guided rotatably to a ring line receiver 5 and the turning force of the rotor 1 is derived from a pinion 7. Projections 1a are made partially in the direction of the thickness of the rotor 1 and brought into contact with the stator 2. Thereby vibration applied to the vibrators is changed over appropriately.