Reinforcing body retainers are formed on an inner peripheral surface near a tip and near a root of first and second claw-shaped magnetic poles. Reinforcing bodies have a trapezoidal base portion and a pair of wing portions formed on two sides of the base portion, and slits are formed completely across a width direction of the base portion at a central portion in a height direction of the trapezoidal shape of the base portion so as to be offset toward a base of the trapezoidal shape. The reinforcing bodies are disposed so as to contact the inner peripheral surfaces of the first and second claw-shaped magnetic poles with a magnet housed and supported in each of the wing portions, and a D ring is fitted into the slits of the reinforcing bodies.