PURPOSE: To eliminate the need for preheating of a copper plate prior to welding by cladding a stainless steel, etc. by build-up welding on the copper plate while melting the same by laser welding thereby forming the boundary part of joining to a narrow wedge shape, and joinning metallurgically strongly.

CONSTITUTION: A filler wire consisting of a stainless steel material (ferritic, austenitic of Ni- and/or Cr-contg. steel material) is built up by laser welding onto the surface of a copper plate 1 in an ordinary temp. without preheating the same to a high temp. A coating layer 2 consisting of the stainless steel is thus formed. The reinforcement of weld of the above-described laser weld zones 2a are superposed on each other so that the joint part between the parts 2a and the plate 1 is made into a wedge shape.