The object of this invention is to have shorter sealing chambers (preheating chamber and gradual cooling chamber) located before and after the brazing atmospheric chamber, to make higher sealing of the atmosphere, and to prevent the scratch caused by the conventional curtains made of metal or others. In order for that, the structures made of steel or graphite are installed standing perpendicular to the moving direction on the conveyor belt which is circulating through the atmospheric furnace. And the bendable or flexible sealing materials are installed on the ceiling and on the right and left side walls of the sealing chambers (preheating chamber and gradual cooling chamber), which are located before and after the atmospheric furnace, into the above two chambers, and making these bendable or flexible sealing materials have rubbing contact with the above mentioned structures.