PURPOSE: To obtain excellent hardness by welding while adding the metal carbide powder not melting with arc heat into the molten pool formed with the arc between welding wire and base metal so as to further harden base metal.

CONSTITUTION: A scattering nozzle 9a is arranged adjacent to the side of advancing direction of a welding torch 7 and a tungsten carbide powder 10 is added to the upper face of a base metal 2 before welding. When the welding torch 7 is moved on the upper face of base metal 2 while weaving in zigzag, arc heat is generated between the welding wire 6 and base metal 2, the welding wire 6 made of soft steel and base metal 2 are melted to form a molten pool 13 and then the tungsten carbide powder 10 added beforehand is mixed. The tungsten carbide powder 10 has a melting point higher than arc heat and remains in powder state while being mixed into the molten pool 13. Thus, by mixing the metal carbide in powder, the base metal is further hardened and its strength is improved as well.