PURPOSE: To improve quality of an ingot by pouring molten steel into shallow mold composing of bottom board and frame body with lining, successively charging molten slag on molten steel surface and slowly solidifying the molten steel from the bottom face toward upper part.

CONSTITUTION: The mold is formed by laying the graphite bottom board 13 at bottom part of a slag pan 11 lining refractory 12. The molten steel is poured into the mold and the molten slag 3 is charged on the surface and then, started to solidify from the bottom face 52 thereof. Then, the solidification to horizontal direction is restrained by heat insulating action of the lining 12 in the slag pan 11 and the heat at the upper part 51 of the molten steel is insulated with the molten slag 3. By this method, the solidification of the molten steel progresses in the form, which interface 53 between solid and liquid formed at almost horizontal ascends as parallel and slow. Therefore, columnar crystal in the molten steel is sufficiently developed and shrinkage pipe in the surface and segregation is prevented and the quality of the ingot is improved.