PURPOSE: To position an electronic part accurately while preventing damage due to solder, and to enable soldering by providing an auxiliary member positioning and inserting the electronic part into an opening section and soldering the electronic part into a through-hole.

CONSTITUTION: Side plates 19a-19c are abutted against an opening section 15 in an auxiliary member 17 and fixed at the fixed position of a substrate 11, and an LED 16 held by the projecting sections 21 of the auxiliary member 17 is fastened temporarily at the fixed position of the substrate 11. When the LED 16 is mounted to the auxiliary member 17, the shape and size of the LED 16 are constrained by the projecting sections 21, thus preventing erroneous insertion. Since the LED 16 is isolated from solder in a solder tank by the auxiliary member 17, it is soldered without receiving damage by heat. Accordingly, solder is not attached by the auxiliary member 17 positioned in the opening section 15 of an extending section 13 and the electronic parts 16 are soldered accurately in the through-holes 14 of a mounting section 12.