Abstract: A soldering apparatus is disclosed which comprises a conveyor for moving print circuit boards along a predetermined path, an inert gas-filling chamber provided with a solder tank wherein the print circuit board is soldered in the inert gas atmosphere, primary and secondary, external air shutoff chambers positioned in front of and in rear of the inert gas-filling chamber, respectively. Both primary and secondary chambers are provided respectively with a first shutter having a mechanism for open/close action and capable of isolating the inside of the chambers from external air and with a second shutter having a mechanism for open/close action and capable of preventing release of the inert gas in the inert gas-filling chamber and are connected through a valve to a vacuum tank capable of evacuating the primary and secondary chambers.