PURPOSE: To make possible cathodic protection at a low cost and to obtain an Al alloy heat exchanger having high corrosion resistance by vacuum brazing a Zn-contg. Al alloy fin material to an Al alloy heat transmission pipe then heating the same in an atm. furnace.

CONSTITUTION: A stage for heating the Al alloy heat exchanger in the atm. furnace after vacuum brazing is added in the stage of producing said heat exchanger by vacuum-brazing the Zn-contg. Al alloy fin material to the Al alloy heat transmission pipe. Then the fin material restores the residual rate of Zn in the surface part and consequently the corrosion potential decreases to the potential enough to provide cathodic protection. The production of the Al alloy heat exchanger having the high corrosion resistance at the low cost is thus made possible.