PURPOSE: To increase the moment of inertia of a rotor and enable the rotor to be stably rotated, by forming the outer rotor with a double cylinder mechanism, on an outer rotor type motor.

CONSTITUTION: A rotor 7 is composed of an internal cylinder 8 and an external cylinder 9. The released end side of the internal cylinder is enclosed with a bracket 10, and the central section of the bracket 10 is fixed on a rotary shaft 5. In close contact with the external side of the internal cylinder 8, a cylindrical winding carrier 11 is concentrically set, and the winding carrier 11 is provided with an armature winding 12. In the meantime, inside the external cylinder 9, rectangular-parallelopiped permanent magnets 13 are radially fixed at specified intervals. The rotor 7 has the internal and external cylinders 8, 9, and so mass units are present at two positions separated from the center of rotation, and so the rotor 7 is to have the great moment of inertia, and the rotation is stabilized with less rotational uniformity.