The present invention relates to a motor, which includes: a rotor portion (1) having a rotational symmetrical body, around which a cylindrical permanent magnet (3) is arranged, and a rotational shaft (6) arranged on an axial line of the rotational symmetrical body; a stator portion (2) having a plurality of stator coils excitable with AC having M phases, which are each arranged on an inner circumference or outer circumference of the permanent magnet to face the permanent magnet; and a bearing portion (5) rotatably and pivotally supporting the rotational shaft to the stator portion, so that the rotational symmetric body and the stator coil are concentric to each other. The permanent magnet includes domains that are magnetized in a radial direction, have aligned magnetizing directions, and are arranged at regular intervals in a circumferential direction. In addition, given that D represents an inner diameter of the permanent magnet, t represents a thickness in the radial direction, N represents the number of domains, and M represents the number of AC phases for driving the motor, D is set to 20 mm or smaller and t is set to satisfy the relation of t ≤ πD/(NM - π).