PURPOSE: To simplify and miniaturize a device to be rotated forward and reverse, by arranging two sets of piezoelectric elements put together coaxially, and by using a torsional converter usable in the forward and reverse rotating directions.

CONSTITUTION: When high frequency voltage is applied to a piezoelectric element 2, then oscillation displacements are generated by the piezoelectric element 2 in the axial direction, and the vertical oscillation displacements are generated by a rod 4 through a horn 3. Accordingly the seat of a torsional converter 10 butted to the upper surface of the rod 4 is vertically displaced, and by the displacement, a rotor 11 is rotated counterclockwise. In the same way, when high frequency voltage is applied to a piezoelectric element 8, then the seat of the torsional converter 10 is vertically displaced by axis-directional oscillation displacements generated on the piezoelectric element 8, and the rotor 11 rotates clockwise.