Abstract: An ultrasonic driven type motor in which an ultrasonic torsional vibrator is activated to generate a forward turning torque for driving a rotor synchronously with the expansion of at least one piezoelectric actuator provided between the vibrator and the rotor, and to generate a return turning torque synchronously with the constriction of the piezoelectric actuator, and the piezoelectric actuator has a coupling control characteristic so that only the forward turning torque is selectively transmitted to the rotor.

Abstract: A rotary driver is disclosed, which comprises a solenoidal oscillation element consisting of an electrostriction element polarized in radial directions or vertical directions and provided with electrodes on pair opposite surfaces perpendicular to the direction of polarization. The electrode on either one of the pair opposite surfaces is uniformly divided by x greater than four. AC voltages of V.sub.o sin .omega.t shifted in phase from each other by 2.pi./x are applied to the division electrodes. A driven member is held in contact with at least one of the opposite surfaces of the solenoidal oscillation element.