The present invention provides a heat exchanger which is assembled by brazing an aluminum fin material to the outer surface of an aluminum tube material formed by bending a sheet material, in particular, an aluminum heat exchanger which can be suitably used as an automotive heat exchanger such as a condenser or evaporator. The tube material is formed of a two-layer clad sheet which includes a core material and an Al--Zn alloy layer clad on the core material. The Al--Zn alloy layer is clad on the outer surface of the tube material and brazed to the aluminum fin material. The potential of the Al--Zn alloy layer in a normal corrosive solution is at least 100 mV lower than the potential of the core material in the normal corrosive solution. The potential of the Al--Zn alloy layer in the normal corrosive solution is lower than the potential of the core material in high-concentration corrosive water. The normal corrosive solution refers to an aqueous solution containing 10 g/l of NaCl and 0.3 g/l of Na.sub.2SO.sub.4, and the high-concentration corrosive water refers to an aqueous solution in which the NaCl concentration is increased by 30 times by concentrating the above aqueous solution.