PURPOSE: To eliminate inverse V segregation of a large-sized steel ingot by providing a casting mold in a pit, feeding water in the pit at the point of the time when 10min elapses after pouring a molten steel therein and releasing the generated steam through a discharge port provided near the head of the casting mold.

CONSTITUTION: A casting mold 2 is installed via double molding boards 6 onto the molding board 4 in a pit 10 and a molten steel 16 is poured through a pouring pipe 8, a runner 18 and a sprue 20 into the mold 2. The molten steel surface is covered by a holding material 22. A steam discharge port 14 provided below a heat insulating material 12 is opened at the point of the time when about 20min elapses after completion of pouring and thereafter cooling water 24 is fed into the pit 10. The water level is maintained in the position below the port 14. The water 24 passes through the space between the mold 2 and the boards 6 and advances into the spacing 28 between the mold 2 and a soldified shell 26 to extract heat from the shell 26. Part of the cooling water is released in the form of steam through the port 14. The inverse V segregation of the large-sized steel ingot is eliminated and porosity defects are considerably decreased by such simple method.