PURPOSE: To allow correction winding and transformer winding and prevent a interlayer short-circuiting of a coil due to high heat, by drawing out the lead of the coil underneath an electrode with solder applied thereto in advance, and by conducting soldering by pushing a heat plate thereto.

CONSTITUTION: Preliminary soldering is carried out by applying solder 30 to an electrode 20, and a bonding agent 40 is applied to the side of a core 10. As for this bonding agent 40, polyamide resin dissolved in an organic solvent, which demonstrates its bonding function fully when heated to about 240°C, is used. A coil 50 is wound around the core 10, and its lead 52 is pulled out downward along the side surface of the core with the bonding agent 40 applied thereto. A heated soldering iron is applied to the bonding agent 40 for one to two minutes to cause the midway of the lead 52 to adhere to the side surface of the core 10. Then, an end part 52a of the lead 52 is immersed in molten solder and placed underneath the electrode 20. A heat plate 60 heated to about 230°C is pushed against the electrode 20 for a few seconds, thereby to heat and melt preliminary solder 30 and resolidify the same. This completes the soldering of the lead end part 52a. Thus, since the core is not immersed in molten solder, there is no possibility of a interlayer short-circuiting of a coil due to high heat.