A brushless motor has a stator and an outer rotor. The stator includes a stator core having 6N teeth and 6N coils wound respectively around the teeth where N is an integer equal to or greater than 1. The rotor includes 6N±2 permanent magnets. The permanent magnets are arranged circumferentially around the stator core and face the teeth across an air gap. The radial thickness of the air gap is uneven along the circumferential direction of the motor.