PURPOSE: To promote rotation efficiency by inserting a bar shaped member into a cylindrical member, moving one center position in the shape of about an arc, and holding contact pressure by the action of magnetic force in a mechanism rotating the other center position by bringing the inside of the cylindrical member into contact with the outside of the bar shaped member.

CONSTITUTION: Four divided electrodes are stuck on a layer-built piezo-electric element 1, a ring 3 is secured to the periphery thereof, a rotor 5 is pivoted on a bearing 6 so that it is capable of rotating, and a permanent ring 4 is slightly longer than the outside diameter of the ring 3, and voltage is applied to the piezo-electric element 1 to rotate the rotor 5. The contact of the ring 3 with the permanent magnet ring 4 is increased by absorbing force, and slippage is reduced.