A soldering apparatus wherein lead pins of a part inserted from above in through-holes of a printed circuit board are soldered to the through-holes from below. The soldering apparatus comprises a solder supplying nozzle, a preliminary heating nozzle and a flux nozzle. Each of the nozzles has an opening and a pair of slits formed to extend downwardly from the opening. The nozzles are moved upwardly and downwardly in a Z direction by respective elevators and are moved and positioned in X and Y directions by a moving table. A printed circuit board to which a lead part to be soldered is temporarily fastened is disposed on the nozzles. As the moving table and the elevators are controlled so that the lead pins projecting to the rear face of the printed circuit board pass through the slits of the nozzles from sidewardly, application of flux to and preliminary heating of the lead pins are performed, and soldering of the lead pins is performed with molten solder supplied to the opening at the upper portion of the solder supplying nozzle.