A welding method for two members adapted to be welded and formed of a low-alloy steel for structural purposes causing the weld metal to develop martensite transformation during cooling after welding, so that the weld metal becomes expanded to a greater degree at room temperature than at a temperature at which the martensite transformation initiates. The welding material comprises a ferrous alloy containing C, Cr, Ni, Si, Mn, Mo and Nb, all of which meet substantially with the contents of the following equation (1): 170≦719−(795×C wt %)−(23.7×Cr wt %)−(26.5×Ni wt %)−(35.55×Si wt %)−(13.25×Mn wt %)−(23.7×Mo wt %)−(11.85×Nb wt %)