A clamper (12) has a clamp finger (12a) for gripping a joint pipe (5), and is preliminarily attached to a preassembly of a heat exchanger. The clamp finger (12a) is deformed to embrace the joint pipe (5), before the preassembly is subjected to the so-called one shot brazing process. Thereafter, the joint pipe (5) is brazed to and become integral with the clamp finger (12a) which is embracing the joint pipe, at the same time as the essential parts incorporated in the heat exchanger preassembly are brazed one to another. Thus, the clamper (12) not only serves as a supporter for keeping the joint pipe (5) in place after the brazing, but also functions as a jig of such a kind as holding in place the joint pipe (5) in the unbrazed assembly of the heat exchanger, thus improving the manufacture efficiency of heat exchangers.