PURPOSE: To eliminate the need for end face finishing of a thin metal plate by filming a granular core metal with coating material in low melting point than core metal, thin metal plate, metal plate to obtain a cladding material, superimposing this cladding material round the thin metal plate, heating and melting it.

CONSTITUTION: A contact part between a corrugated heat exchanger element 1 of thin metal plate and a partition board 10 is coated with the cladding material 22. The cladding material 22 is clad grains obtained by plating a core metal 20 with coating material 21. The coating material 21 is lower in melting point than the core metal 20, the thin metal plate 1, the metal plate 10. For example, the coating material 21 is of Ni and the others are of stainless steel. The grains of the cladding maternal 22 are uniform and superimposed by giving a vibration to the partition board 10 brazing furnace having a vacuum atmosphere. The coating material 21 is melted by this heating, acts as brazer and joins the partition board 10 and the element 1 through the core metal 20. A flow path is not choked with overflow of the brazer. The need for finishing accuracy of the end face of the element can be eliminated.