The stator 3 is provided with a magnet 4 (permanent magnet) for forming a magnetic field to be applied to the rotor 6. The magnet 4 has p pairs of magnet magnetic poles 5 formed in a curved surface shape. A shape of the magnet magnetic pole 5 is, for example, an arc surface shape or a shape similar thereto. The magnet magnetic poles 5 are attached along an inner peripheral surface of the housing 2 and arranged at predetermined intervals in the circumferential direction (circumferential direction of a circle centered on the rotation axis C in a cross section perpendicular to the rotation axis C). An orientation of a magnetic field is set to a direction from the outside to the inside of the housing 2 or the opposite direction (direction from the inside to the outside). In the present disclosure, the magnet magnetic poles 5 are arranged such that orientations of the magnetic fields are reversed between the adjacent magnet magnetic poles 5.