Resin pooling grooves are disposed so as to extend over entire regions in a thickness direction of a first magnet holder on two sides of a bottom surface in a width direction of a first receiving groove, and resin pooling grooves are also disposed so as to extend over entire regions in the thickness direction of the first magnet holder on two side surfaces of the first receiving groove near the bottom surface. A first resin injection aperture is disposed through the first magnet holder so as to communicate with the resin pooling grooves over an entire region in the thickness direction. A first permanent magnet is held by the first magnet holder by fitting the first permanent magnet into the first receiving groove together with a first magnet cover, and injecting a resin material into the resin pooling grooves through the first resin injection aperture and hardening it.