To provide a proper electric resistance value for a heating wire, reduce unfavorable electric resistance values, and improve the yield by a method wherein an electric resistance of the wound heating wire is measured, and a tension of the heating wire in a winding process is changed based on the electric resistance value.

Right after an electric welding joint 100 which is a formed article, is separated by dividing a core 10, an electric resistance value between terminals is measured. Then, based on the electric resistance value, a tension of a heating wire of a heating wire winding device is corrected and changed. More in concrete, when the electric resistance value measured right after the separation from the core 10 is smaller than a target electric resistance value, the tension in the winding process is increased, and when the electric resistance value is larger than the specified value, the tension is decreased. Thus, the following manufacture is performed, and the manufacture which is performed after that is changed in such a manner that the tension may become the target electric resistance value.