Brushless DC motor

In a brushless DC motor constructed by a rotor 2 to which a permanent magnet 3 is attached; and a stator 1 having a plurality of slots, when an effective opening angle of magnetic pole of the rotor 2 that was set to a predetermined opening angle whose base is the rotation axis of the rotor 2 is theta2 and a salient area opening angle of magnetic pole formed within the effective opening angle theta2 of magnetic pole is theta3, the opening angles theta2 and theta3 are set so that cogging torque generated by the effective opening angle theta2 of magnetic pole and cogging torque generated by the salient area opening angle theta3 of magnetic pole are mutually in antiphase. Accordingly, a brushless DC motor capable of reducing cogging torque is realized.