PURPOSE: To suppress the eddy current and to obtain stable characteristics with high efficiency by using Fe-Si alloy of a predetermined content or less of added amount of Si for a predetermined yoke.

CONSTITUTION: First to fourth stator yokes 5 to 8 are concentrically disposed on the periphery of a rotor 4. More particularly, a first phase is formed of the first and second yokes 5, 6, and a second phase is formed of the third and fourth yokes 7, 8. The yokes 5 to 8 are bent at the inner peripheries of the ringlike flanges 5a to 8a of the flat plate by 90 degrees in a predetermined direction to form pectinated poles 5b to 8b. Any of the four yokes 5 to 8 is formed of Fe-Si Alloy containing predetermined composition content (added amount of 2.0% of Si where the alloy is bendable and excellent characteristics).