An alternator for a vehicle is provided which is equipped with a heat dissipator and a cooling air generator. The heat dissipator is disposed in a rectifier to cool rectifying devices. The cooling air generator generates a flow of cooling air to the heat dissipator. The heat dissipator has a plurality of sub-fins formed thereon. Each of the sub-fins is defined by a combination of a protrusion and a recess. The protrusions are formed on one of opposed major surfaces of the heat dissipator, while the recesses are formed on the other major surface, one in coincidence with each of the protrusions in a thickness-wise direction of the heat dissipator. This permits the heat dissipator to be pressed to form the protrusions and the recesses to make the sub-fins simultaneously, thus allowing a heat-dissipating area to be increased to ensure a desired degree of heat capacity thereof.