A rotor for a vehicular alternating current generator has a relief space portion formed between axial holes of a pair of pole cores and a shaft for receiving therein a plastically deformed portion produced when the shaft is press-fitted in the axial holes of the pole cores. The relief space portion is located adjacent to a pair of closely contacting inner end faces of the pole cores so that the plastically deformed portion is let to move into a radially outward direction rather than further continuing movement in an axial direction within the relief space portion. The plastically deformed portion is thus prevented from entering between the inner end faces of the pole cores.