An aluminum alloy heat exchanger with aluminum alloy tubes is provided by assembling and brazing. A coating which includes from 1 to 5 g/m2 of Si powder, from 3 to 20 g/m2 of Zn containing flux, and from 0.2 to 8.3 g/m2 of binder is formed on the aluminum alloy tubes. The fins contain Zn and 0.8 to 2.0% by mass of Mn, Si in a ratio of 1/2.5 to 1/3.5 relative to the Mn, and less than 0.30% by mass of Fe. A fillet is formed between the tube and the aluminum alloy fin after brazing, and a primary crystal portion is formed in the fillet. A eutectic crystal portion is formed in a portion other than the primary crystal portion, and the electric potential of the primary crystal portion is equal to or higher than the electric potential of the aluminum alloy fin.