PURPOSE: To reduce the magnetic leakage gap between a stator and a rotor by stopping the slot sections of stator core to a plurality of axial ribs formed integrally on the outer circumference of a can.

CONSTITUTION: A can 4 is molded of synthetic resin and a plurality of axial ribs 14 are formed integrally on the outer circumference with approximately identical interval in the circumferential direction. A stator 13 has a plurality of slot sections 16 in the core 15 to be mounted with a winding, and each slot section 16 is stopped to an axial rib 14 at an opening 16a extending in the axtial direction. The can 4 can be made thin through the axial rib 14 arranged on the outer circumference and the magnetic leakage gap between the stator 13 and the rotor 8 can be reduced correspondingly.