PURPOSE: To prevent the degradation in a brazing by a treating object or working environment by blowing gaseous nitrogen contg. fluorine into a salt bath to make up the deterioration in the acidity of the bath.

CONSTITUTION: An aluminum or aluminum alloy member previously attached with a brazing filler metal is dipped into the salt bath consisting of an inorg. salt contg. fluoride and is subjected to salt bath brazing. The gaseous nitrogen contg. the fluorine and/or fluoride is, thereupon, blown into the salt bath to make up the deterioration in the acidity of the bath and to restore the reducing property. Powders of, for example, BaCl, NaCl, KCl and KAlF4 are mixed and the mixture is melted in an electrode furnace and is used as the inorg. salt. As a result, the salt bath for aluminum brazing consisting of the inorg. salt contg. the fluoride deteriorated with lapse of time is again purified.