PURPOSE: To form a bundling yarn of a material made of lower oligomer and having strong tensile strength.

CONSTITUTION: Coil ends 11 of a winding 10 are bundled by a bundling yarn 12. The yarn is formed of yarns formed of filaments of polymer polyester. Thus, the quantity of oligomer to be extracted from the yarn 12 is reduced, clogging of the oligomer is suppressed, and a tensile strength of the yarn for bundling the coil ends is improved.