PURPOSE: To execute a work with a high efficiency and to obtain a product having a high accuracy by filling a fluid having a light shielding property, between a glass plate which has been placed so as to cover a lead part of flat lead parts on a substrate, and the substrate, and irradiating a laser light through the glass plate.

CONSTITUTION: On a printed circuit board 1, flat lead parts 3 are placed, and a glass plate 10 is placed so as to cover a lead part 4 of flat lead parts 3. Subsequently, a fluid having a light shielding property is filled between the glass plate 10 and the printed circuit board 1. Next, a laser light 6 is irradiated and scanned to the lead part 4 through the glass plate 10. As a result, the lead part 4 is heated selectively, and soldering 12 can be executed between the lead part 4 and the printed circuit board 1. According to this method, the work efficiency is improved and soldering can be executed with a high accuracy.