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.