PURPOSE: To lessen a possibility that a conductor foil is broken or wrinkles and to contrive to make possible a high-speed winding work.

CONSTITUTION: A thermosetting bonding agent 51 put in a container 5 is applied on the surface on one side of the surfaces of a conductor foil (an aluminium foil) 2 via rollers 52 and an insulating film 31 is closely adhered to the surface on one side by a roller 41 and thereafter, the foil is heated by a heating roller 6 to harden the bonding agent, whereby the foil 2 is reliably constituted integrally with the film 31. This integrally constituted material is applied a prescribed tension by rollers 42, is superposed in order in the radius direction of a winding machine 10 and is wound on the machine 10. As the tensile strength and thickness of the integrally constituted material of the foil 2 with the film 31 are respectively the sums of the respective tensile strengths and thicknesses of the foil 2 and the film 31, the foil 2 is hardly broken and hardly wrinkles. As a result, it becomes possible that the number of rotation of the integrally constituted material at the time, when the integrally constituted material is wound by the machine 10, is increased and a working efficiency is improved. Moreover, as no gap is formed in the adhesive surface of the foil 2, an effect of the improvement of a heat conduction efficiency in the radius direction of a sheet coil 1 is also obtained.