In a stator core having “N” slots, a tooth-width centerline of a linear yoke and a first extension line extended horizontally from a center of rotary shaft toward the linear yoke form a first angle. Assume there are first point on the first extension line at a first distance from the center, a second extension line drawn at a second distance horizontally from the center toward the linear yoke and extended vertically toward arc-shaped yokes, and a third extension line drawn from the center toward teeth ends of the linear yokes with angle “K”. The second and third extension line intersect at a second point. A line between the first and second points intersects with the first extension line, thereby forming the first angle. In this structure, 0