PURPOSE: To improve the corrosing resistance by specifying the difference in the concentrations of Cu of the core material of a brazing sheet and the skin material surface, specifying the concentration of Cu of the skin material surface and forming the Zn diffused layer in specified concentration on the skin martial surface.

CONSTITUTION: A heat exchanger made of Al takes the Al alloy containing ≥0.3% Cu as the core material and refrigerant passages 9, 9' are composed of the brazing sheet cladded with an Al alloy brazing filler metal on one side thereof and Al alloy brazing filler metal or Al alloy lining material on the other side as the skin material. In this heat exchanger, the concentration difference of Cu in the core material of the brazing sheet composing the refrigerant passage and the skin material surface is used at ≥0.2% and the concentration of Cu of the skin material surface at ≤0.2% and further the Zn diffused layer having ≥0.3% concentration of Zn is formed on the skin material surface.