PURPOSE: To prevent noise without stirring surrounding air when a rotor for drive is rotated by providing a thin cylindrical part which is formed by extending a salient pole tip surface in peripheral direction at the rotor for drive.

CONSTITUTION: Tip edge surfaces 4A, 4B,... of salient poles 4a, 4b,... which are provided at a rotor for drive 4 are provided at thin cylindrical parts 7a, 7b,... which are extended in the peripheral direction. A surface is flattened by burying a non-magnetic and non-conductive material into spaces 6a, 6b,... which are surrounded by 4a, 4b,... and the thin cylindrical parts 7a, 7b,... or by covering with a plate. Therefore, by forming a surface opposing to stator magnetic poles 2a and 2b of a rotor for drive 4 into a one-piece cylindrical surface without any recessed or projecting parts over an entire periphery, no surrounding air is stirred by the salient pole and no noise is generated when the rotor for drive is rotated.