A motor comprises a stator and a rotor (20) disposed within the stator. The stator comprises: a housing (31) having a polygon cross section that comprises a plurality of side portions (32a-32d) and a plurality of curved corner portions (33a-33d), each of the corner portions connect two adjacent side portions and curve around a center (O′) which is offset from the rotational center (O) of the rotor; and a ring magnet (34) fixed to the inner surface of the housing. An air gap (37) is formed between a peripheral surface of the rotor (35) and an inner surface of the ring magnet (34). The thickness of the ring magnet at portions corresponding to the corner portions (33a-33d) of the housing being larger than the thickness of the ring magnet at portions corresponding to the side portions (32a-32d) of the housing.