A soldering apparatus including a vessel containing a molten solder, a casing defining therewithin a soldering chamber in which a flat overflowing wave of the molten solder is formed, a conveyor physically integrated with the casing for movement therewith and operable for transferring a printed circuit board through the soldering chamber, actuators and for vertically moving the casing, inert gas feeders for feeding an inert gas to the soldering chamber, and a controller for controlling the operation of the actuators and, so that the printed circuit board is contacted with the surface of the flat overflowing wave in an atmosphere of the inert gas during its passage through the soldering chamber.