PURPOSE: To increase the torque by adding the contacting force of a movable body with a driver by using a shape memory alloy for the body.

CONSTITUTION: A piezoelectric unit 1 made of piezoelectric ceramic for exciting a traveling wave to a circular driver is polarized in the thicknesswise direction, and a plurality of electrodes 2 are formed in the same direction. The outer periphery of the unit 1 is bonded to the elastic material 3 formed with an uneven part on the outside to form a driver 4. A movable body 5 made of nickel- titanium shape memory alloy which exhibits elastic elongation, i.e., quasi- elasticity due to a Martensite transition is disposed outside the driver 4 to always clamp the driver 4 in a radial direction. When an electric field is appled to the unit 1, a longitudinal traveling wave of bending vibration is excited in the circumferential direction of the driver 4, and lateral traveling wave combined with the longitudinal wave is transmitted to the material 3 to rotate the body 3.