A mold used in a manufacturing process of a rotor of an electric motor, the rotor including a rotor core with a plurality of magnet-retaining apertures and a plurality of permanent magnets individually retained in the magnet-retaining apertures of the rotor core, for pouring a resinous material into gaps defined between the magnet-retaining apertures and the permanent magnets. The mold includes a cavity for accommodating the rotor core at a predetermined position, with the rotor core receiving the permanent magnets individually in the magnet-retaining apertures; and a deformation inhibiting surface provided in the cavity and coming into at least local contact with an outer circumferential surface of the rotor core, during a period when the resinous material is poured into the gaps, to inhibit the bulging deformation of the outer circumferential surface.