The present invention relates to an Al alloy brazing sheet for use in vacuum brazing, which is applied to manufacture a heat exchanger having a tank portion and a refrigerant passage respectively formed by bonding press-formed brazing sheets together by means of vacuum brazing. The brazing sheet includes an Al alloy core material having a composition consisting of 0.5 to 2.0 mass % (hereinafter abbreviated simply as %) of Mn, 0.1 to 1.0% of Cu, 0.05 to 0.5% of Mg and 0 to 0.3%. of Ti, with the remainder being Al and inevitable impurities. An Al--Si--Mg alloy brazing filler metal or an alloy brazing filler metal prepared by further adding 0.05 to 1.0% of Sn to the Al--Si--Mg alloy brazing filler metal, is clad on both surfaces of the sheet to a thickness of 5 to 20% the total sheet thickness. An intermediate layer consisting of an Al alloy having a composition consisting of 0.5 to 2.0% of Mn, 0.05 to 0.5% of Mg and 0 to 0.3% of Ti, with the remainder being Al and inevitable impurities, is provided between the core material and the brazing filler metal corresponding to the outside of the tank portion and the refrigerant passage and has a thickness of 30 .mu.m or more, preferably 80 .mu.m or more, and 35% or less of the total sheet thickness. This Al alloy brazing sheet provides excellent outside corrosion resistance for the heat exchanger.