Abstract: A wound core, around which electric wires are wound by rotating cylindrical bobbins attached. At least one of a winding start portion and a winding end portion is formed into a trapezoidal cross-sectional shape and the other portion is formed into a circular cross-sectional shape, forming a gap between the trapezoidal cross-sectional shape portion and the bobbin. The rotation of the bobbin without scratch is assured even if the wound core is formed slightly deformed. In cutting-off the material, since the magnitude of the directional change of the cutting tool is decreased at the trailing end and the leading end of the material, the cutting speed is improved.