To obtain a small-sided motor at a low cost which can obtain large torque at a low rotational speed region, and obtain a motor which can restrain rotation irregurality of a photosensitive drum without increasing size and cost of an image processor.

This synchronous reluctance motor 10 has outer rotor structure which is equipped with a stator 12, a rotor 30 and a slit group 34, and is suitable for a low speed motor having large torque wherein rotational inertia force of the rotor 30 is large. In the stator 12, a coil 22 is wound around a plurality of slots 20 which are arranged radially and opened outward. The rotor 30 has a cylindrical rotor core 32 composed of magnetic substance, and the rotor core 32 is rotatably arranged outside the radial direction of the stator 12. The slit group 34 consists of a plurality of concentrically circular arc type slits 36 which are arranged at an equal interval along the peripheral direction of the rotor are core 32 and recessed on the axial line side of the stator 12.