A rotor includes S-pole and N-pole magnets which are arc-shaped in cross-section. Each pole has three magnets. Each magnet is embedded in the rotor in such a way that a convex side portion thereof faces center Or of the rotor. Distance Rs between center Os of circular arcs of S-pole magnets and center Or of the rotor is different from distance Rn between center On of circular arcs of N-pole magnets and center Or of the rotor (Rs≠Rn). The ratio of the two distances is 0.92 (Rs/Rn=0.92). An outer peripheral section of an innermost-layer S-pole magnet is disposed in such a way as to protrude into an adjacent pole zone N1 or N2 from a pole zone S1 or S2.