A rotor core is configured by arranging divided rotor cores coaxially so as to be in close contact with each other such that magnetic pole centers are aligned axially, auxiliary grooves are recessed into respective outer circumferential surfaces of the divided rotor cores between respective magnetic poles so as to have plane symmetry relative to a plane that includes a center position between the magnetic poles and a central axis of the divided rotor cores, and so as to extend from a first axial end to a second axial end of the divided rotor cores, the auxiliary grooves recessed into an outer circumferential surface of an identical divided rotor core have an identical groove shape, and groove widths of the auxiliary grooves are set such that predetermined orders of harmonic components of cogging torque that result from each of the divided rotor cores mutually cancel each other out.