Abstract: A stator assembly operated in a 2-phase drive manner including first and second stator coils wound in a star shape with a plurality of projections and a plurality of grooves, and arranged with a predetermined phase difference; and an annular supporting body into which the first and second stator coils are inserted for supporting the coils, insulating them from each other. Each stator coil includes four projections and four grooves, and there is a phase difference .theta. between the first and second stator coils, the difference determined by the following equation: .theta.=360/2P.+-.360/P, wherein P denotes the number of a rotor's magnetic poles.