A brushless DC motor prevents disconnection of a magnetic flux and to minimize leakage of the magnetic flux, thereby reducing torque ripple. A plurality of magnetic flux-disconnection preventing holes are arranged in an outer periphery of a rotor core between installing holes into which magnets are fitted. The plurality of magnetic flux-disconnection preventing holes are symmetrical at both sides about a first line connecting a center of the rotor core to a center between the adjacent installing holes, and an angle between the first line and a second line connecting the center of the rotor core to an outermost end of the plurality of magnetic flux-disconnection preventing holes is about 15˜20°. A length between an outer periphery of the rotor core and an outer periphery of the plurality of magnetic flux-disconnection preventing holes is smaller than a gap between the rotor core and the stator.