The present invention comprises a permanent magnet (13) that is disposed around a rotor shaft (11), a retaining ring (14) that is press-fitted around the outside of the permanent magnet (13) from one end of the rotor shaft (11) so as to retain the permanent magnet (13) against the rotor shaft (11), and an end plate (12) that is provided adjacent to the permanent magnet (13) in the axial direction of the rotor shaft (11) and guides the press-fitted retaining ring (14), maintaining planar contact with the inner circumferential surface thereof, toward the permanent magnet (13) while causing the retaining ring (14) to expand as the retaining ring (14) progresses from one end of the rotor shaft (11) to the other end of the rotor shaft (11). Concentration of stress on the retaining ring (14) during press-fitting can thus be minimized.