To reduce manufacturing cost significantly by pressing a stainless steel plate to produce a heat transfer plate of specified shape, and plating it with a metallic material suitable for soldering to form a metal film on the entire surface so that welding can be made in an ordinary continuous deoxygenation electric furnace.

A specified number of heat transfer plates 10 for exchanging heat by conducting two kinds of fluid through upper and lower layers separated by one layer sectioned by the upper and lower heat transfer plates 10 by fitting a protruding edge 17 in an upper stage opening 15 are stacked fixedly and welded in an ordinary continuous deoxygenation electric furnace. Since an alloy layer of stainless and metal coating can be formed by welding the metal coating at the part where the upper and lower heat transfer plates 10 touch in the furnace, rigid welding is realized. Furthermore, gastight joint can be realized because the circumferential fringe part is welded at the side edge part 11.