A welded portion shape of a cross-section perpendicular to the shaped steel longitudinal direction is set to satisfy a>0 mm, b>0 mm, c≥0.14 Tw, d≥0 mm, e≥0 mm, a+d≤2 mm and b+e≤2 mm; where a is a front melting width of the web material (on the laser beam irradiation side), b is a rear melting width of the web material (on the laser beam non-irradiation side), c is a maximum weld penetration depth, in a plate pressure direction, into the flange material, d is a front melting width of the flange material (on the laser beam irradiation side), e is a rear melting width of the flange material (on the laser beam non-irradiation side), and Tw is the plate thickness of the web material.