A coil assembly of a stator is configured in such a manner that an air core region of each magnet coil houses effective coil parts of different magnet coils. The outer shape of each magnet coil in a section perpendicular to a center axis of a rotor is a divided ring-like shape defined by dividing a circular ring into equal N parts. Two sides of the divided ring-like shape form an angle set to be 360°/N or less. Each magnet coil is made of a coil conductive wire including a conductive wire bundle as a bundle of multiple non-insulated conductive wires each being a non-insulated wire, and an insulating coating layer covering the periphery of the conductive wire bundle.