PURPOSE: To prevent the damage of an insulating sheet even when a foreign matter is mixed by making the hardness of a metallic sheet lower than that of the insulating sheet and increasing the elongation percentage of the insulating sheet.

CONSTITUTION: A material having hardness lower than the hardness of an insulating sheet 12 is used as a metallic sheet 11, and a material having a large elongation percentage is employed as the sheet 12. Consequently, when a foreign matter 13 is mixed between wiring turns, the sheet 12 wraps in the foreign matter 13 and closely adheres on the outer circumferential surface of the sheet 11, but only a foreign matter 13 section is projected to the outside because the elongation percentage of the sheet 12 is large. When the next turn is wound, a projecting section by the foreign matter 13 is absorbed by the sheet 11, and the sheet 12 is subject to only deformation by elongation and mechanical break by surface pressure during winding is not generated.