PURPOSE: To produce a large sized steel ingot having no segregation and having a specific height and a specific height to diameter ratio by installing a molding flask made of steel plates mounted with a heat insulating material on the outer side on a molding board made of metal, charging molten steel into the molding flask, taking up the heat insulating material at a specific speed and allowing the molten steel to solidify.

CONSTITUTION: In the stage of producing a large sized steel ingot having a circular or rectangular section of ≥1m height and ≥1 height to diameter ratio, a molding flask 2 made of steel plates having about 5W20mm thickness is installed on a molding board 1 made of metal having good heat conductivity. A heat insulating material 3 having fire resistance is held with an outer flask 4 and is mounted on the outer side of the flask 2. Molten steel 5 is charged into the flask 2 and the upper part is covered with a heat insulating material 6. Then the material 3 is taken up at 0.1W2.00mm speed per minute together with the flask 4 by means of chains or the like to allow the molten steel 5 to cool and solidify slowly from below to upward while suppressing the solidification thereof from the side surface. Thus the large sized steel ingot of the uniform structure is obtained without segregation in the axial central part as well.