PURPOSE: To prevent the dripping of unhardened resin section as well as to improve the characteristics of withstand voltage and damp-proof property of the subject device by a method wherein a light and heat curing type resin is impregnated into the wound section and after the resin has been light-cured, it is heat-cured.

CONSTITUTION: A wound section 27 is formed by winding the primary winding A and the secondary winding B on the bobbin 20 having flange sections 21 and 28. Within this wound section 27, and light and heat-curing type resin 29 is filled in fully and then a beam of light is irradiated at the wound section 27, and the resin 29 located on both end surfaces 27a and 27b in the wound section 27 and on the outer circumferencial surface 27c is light-cured in such a manner that the nonhardened heat-curing type resin 29 section among the resin 29 is surrounded. Then heat is applied on the wound section 27 and the entire resin 29 is solidified. Thus, the dripping of the nonhardened resin onto the outer section of the wound section 27 is prevented and whole of the injected resin can be solidified, thereby enabling to improve the withstand voltage and damp-proof characteristics.