To solve the problem that the temperature rise by heat is raised by the increase of a coil resistance in a narrow width part from that the sectional area of the narrow width part becomes smaller than that of the other part since the wound coil having a small curvature part is formed by curving a flat wire at the narrow width part by forming the narrow width part having a relatively narrow width with a predetermined interval in the longitudinal direction of the flat wire in the wound coil.

A cylindrical conductor consisting of blocks which can be engaged with the teeth is cut spirally between cut surfaces in response to the thickness of the flat wire to form the flat wire. Thus, its coil resistance is not increased, and the temperature rise by the heat is prevented as well.