PURPOSE:To increase the cooling air amount and to increase the output of a generator by providing centrifugal fans at both sides of a rotor, and fixing a fan guide at a clamping bolt for clamping a rectifier mounted on a rear bracket. CONSTITUTION:Centrifugal fans 8a, 8b are fixed by a projection welding or the like to both sides of rotor cores 7a, 7b the first fan 8a intakes cooling air by its rotation from a vent hole 1a for intaking the cooling air of a front side bracket 1 to cool a stator coil 3b and to exhaust it from a vent hole 1b for exhausting it as an arrow A. The second fan 8b intakes cooling air from a vent hole 2a for cooling and intaking a rear bracket 2 to cool an IC regulator 10, and a 3-phase full-wave rectifier 11 and to exhaust from the vent hole for exhausting while cooling the coil 3b as arrows B, C. In this manner, the cooling air flow rate can be increased, thereby increasing the output of a generator.