In an automotive alternator having a case in which air intake vents 1a and air discharge vents 1b are disposed, a rotor, which is fastened to a shaft such that claw-shaped magnetic poles intermesh, has as a pair of fans having a plurality of blades and fastened to the axial end surfaces of poles cores, and is rotatably disposed in the case, a stator core to which a plurality of slots are formed and a stator having a stator winding to be accommodated in the slots, the slots are formed in an even number, each of the claw-shaped magnetic poles is formed in an even number, and said blades of the pair of fans are formed in the same odd number, respectively. With this construction, there can be provided a small automotive alternator which has a high output and an excellent cost performance and in which fans generate a low level of noise.