In an AC generator for a vehicle, an end cover has two types of parts, one-type part is away from a rib part in a positive cooling fin, and the other-type part is close to the rib part. The rib part projects toward the end cover side. The one-type part is thinner than the other-type part in the end cover in order to reduce the variation of thermal expansion in each part of the end cover. This configuration increases anti-thermal fatigue of the end cover.