The lower layer coil arm 536 and the two lower layer coil ends 537, like the upper layer coil bar 531, may be a member integrally molded by cold casting, may be a member shaped by bending in a press into a U-shape, or may be a member formed by joining a lower layer coil arm 536 and 2 lower layer coil ends 537 made as separate parts by a joining method such as welding.