PURPOSE: To produce a steel for welded structure excellent in weld zone as well as in base material by regulating oxygen content in a molten steel having a specific composition consisting of C, Si, Mn, N, and Fe, adding specific amounts of Ti, and further adding specific amounts of Al at the time of casting.

CONSTITUTION: The content of oxygen in a molten steel which has a composition consisting of 0.02-0.20% C, 0.02-0.20% Si, 0.50-2.00% Mn, 10-60ppm N, and the balance Fe with inevitable impurities and further containing, if necessary, one or more kinds among 0.05-1.00% Cu, 0.05-1.00% Ni, 0.05-1.00% Cr, 0.03-0.50% Mo, 0.005-0.050% Nb, 0.005-0.050% V, and 0.0005-0.0030% B is regulated to 20-200ppm. Subsequently, 0.005-0.030% Ti is added to this molten steel. Further, at the time of casting, 0.010-0.100% Al is added to this molten steel in a tundish or in a mold. The resulting cast bloom is heated and rolled by the ordinary method. By this method, a Ti oxide is sufficiently formed and also an Al nitride is formed, by which the steel for welded structure excellent in toughness in large heat input welded joint as well as in base material can be obtained.