An improved construction of a .�.Randel.!. .Iadd.Lundell.Iaddend.-type rotor of a vehicle-mounted alternator, capable of reducing the windage noise which is produced as a result of interference between the rotor and the stator of the alternator. The rotor has a pair of pole cores provided with a plurality of mutually meshing claws, and an exciting coil disposed at the inner side of the pole cores. Spacers in the form of an integral ring or discrete wedges are fitted in the spaces between adjacent pole core claws so as to provide a substantially smooth cylindrical outer peripheral surface of the rotor portion facing the radial teeth on the stator.