In order to prevent poor operability caused by entanglement of the fins in the heat sink during assembly without a drop in the cooling efficiency of the cooling flow along a rotation shaft, a plurality of fins 23c of the heat sink in a vehicle AC generator 1 is constituted by fin groups 123 in which fins are aligned in parallel in one direction, and an entanglement preventing portion 23d is disposed only on the respective outer side surfaces of a pair of outermost fins.