PURPOSE: To restrain a solder amount attaching to a root part of a lead and to prevent shortcircuiting between adjacent leads by providing a preliminary soldering jig, a fitting part for fitting a jig, a holder having a holding screw, etc.

CONSTITUTION: A lead 3-2 of a QFP part (electronic part) 3 is inserted and a package side of a package 3-1 is brought into contact with a preliminary soldering jig 14. An end edge of the jig 14 is fit to a fitting part 15-1a formed in one end side of a frame 15-1 of a holder 15. Then, an upper surface of the part 3 is pressed by a holding screw 15-2 to project a junction surface of the lead 3-2 by a fine dimension, to hold the jig 14 and to immerse a junction surface of the lead 3-2 in molten solder 2 of a solder pot 1 by making the jig 14 horizontal. The molten solder 2 creeps and rises on a surface of a lead 3-2 of good wettability; however, an insertion hole 14a formed of a material having property to repel molten solder away enclosing an outer periphery of the lead 3-2 restrains the solder 2 from rising to a root part of the lead 3-2 and prevents shortcircuiting between adjacent leads 3-2.