Disclosed is a magnetic flux concentrated-type brushless motor performing field weakening control and reducing iron loss. The teeth of the stator are provided with a stator-side wide-width portion, and the rotor is provided with magnetic members having a rotor-side wide-width portion, and magnets disposed between the magnetic members. The motor is driven for a certain time in a low rate of rotation (LRR) section and a high rate of rotation (HRR) section. Field weakening control is performed in the HRR section. When the number of pairs of opposite poles of the rotor is P, a length of a radial line of the rotor-side wide-width portion R, a thickness of the stator-side wide-width portion Lt, a central angle of the stator-side wide-width portion τt, a central angle the rotor-side wide-width portion τr, and a central angle between any two neighboring magnets τM, the motor is set such that τr≦2.85×τm−2.65×τt and (Lt×P)/(ττ×R)≧τt/τm−0.6.