A motor/generator (1) comprises a permanent magnets (3) having a V-shaped surface projecting in the center of a rotor (2). These permanent magnets (3) are disposed so that the V-shaped surface faces the center of the rotor (2). In this way, the permanent magnets (3) are prevented from sliding on the fitting surfaces (21) of the insertion holes (20), and the permanent magnets (3) can be fixed at predetermined positions. Further, magnetic losses caused by the rotor (2) can be reduced, and efficiency of the motor/generator can be improved.