A rotor 31 has permanent magnets 31a disposed on a surface of a disk-shaped back yoke 31b in such a manner that long sides of each permanent magnet extend in a radial direction and that a South pole and a North pole of the permanent magnet 31a are arranged in a circumferential direction. The four permanent magnets 31a are equally spaced from one another in the circumferential direction, and circumferentially-opposed magnetic poles of any two adjacent permanent magnets 31a are of the same magnetic polarity. Rotor cores 31c of a generally fan-shape are fixed to the back yoke to generally cover the four permanent magnets 31a. A flux barrier 31d for reducing the short-cutting of magnetic flux of the permanent magnet 31a is provided between any two adjacent rotor cores 31c, and is disposed at a radially-extending central portion of the permanent magnet 31a.