PURPOSE:To improve the centrifugal force resistance and to increase the cooling efficiency of an AC generator by previously forming a fan flat part along the round of a pole core. CONSTITUTION:A rotor coil 6 is held to hold opposite two pole cores 3, which are integrally engaged by a knurl formed on the surface of a shaft 10. A front fan 4 and a rear fan 5 are held by a suitable method on both end faces of the core, and a rotor 7 is formed as a whole. A stator 1 is disposed on the outer periphery of the rotor. The outer periphery of a fan blade 9 is previously bent in the same or slightly larger than the shape of the round 8 of the core 3, secured to the end face of the core 3, and a bent part 8a is formed so that both are closely contacted at the rounded parts.