PURPOSE: To simplify a structure and to inexpensively manufacture by enclosing a general-purpose rotating speed detector mounted on one end face of an electric rotating machine body with a cover having a pressure resistant explosion-proof structure of a U-shaped section mounted on one end face of the body.

CONSTITUTION: A general-purpose rotating speed detector 13 is mounted directly on one end face of a rotary electric machine body 11, and a rotary unit of the detector 13 is mounted directly on the end of a rotary shaft 14. The detector 13 is contained in a cover 16 having a pressure resistant explosion-proof structure of a U-shaped section mounted on one end face of the body 11. Thus, the number of components is reduced, the detector is used, its structure is simplified, and its cost is reduced.