PURPOSE: To shorten an axial length and to reduce size and weight by providing cores at vibration plates disposed oppositely to each other.

CONSTITUTION: Vibration plates 7a, 7b disposed oppositely with a rotor 6 as a center, tiltably supported axially with a rotary shaft 5 as a fulcrum, for holding the part of the circumferential end of the rotor 6 at the time of tiling are provided. Cores 11a, 11b having windings 13a, 13b disposed at a predetermined interval along the circumferential direction at the circumferential ends of the plates 7a, 7b and so excited as to operate an attraction force at the half faces of the plates 7a, 7b and a reaction force at the other half faces are provided. Accordingly, a circumferential length difference is generated between a distance from the shaft 5 to the rotor 6 and a distance from the shaft 5 to the plates 7a, 7b in a section in which the rotor 6 is brought into contact with the plates 7a, 7b. When the exciting state of the winding is sequentially varied in an arbitrary direction by holding the circumferential length difference, the rotor 6 is slowly rotated reversely. Thus, the rotor 6 can be reduced in size, and its vibration can be decreased.