PURPOSE: To produce a thick steel plate having high strength and toughness, free from deterioration in the properties in a weld zone and a weld heat-affected zone, having corrosion resistance, and suitably used for a stock for line pipe, at a low cost without causing reduction in productivity.

CONSTITUTION: A continuously cast slab, having a composition consisting of, by mass, 0.02-0.10% C, 0.03-0.15% Si, 1.00-2.00% Mn, 0.001-0.050% sol.Al, 0.005-0.025% Ti, 0-0.0050% Ca, either or both of 0.005-0.060% Nb and 0.02-0.10% V, two or three kinds among 0.15-0.50% Cu, 0.20-1.00% Ni, and 0.15-0.40% Mo, and the balance Fe with impurities, is used as a stock. This stock is heated at 1100-1200°C, rolled at a temp. between Ar3 and (Ar3+100)°C at 30-80% draft, finish-rolled at 650-850°C, cooled without delay down to room temp. at ≥20°C/s cooling rate, and then tempered at 450-650°C.