PURPOSE: To reduce the surface effect and obtain an excellent steel ingot by laying a top part heat insulating board on upper edge of an ingot case, pouring molten steel and igniting and burning the top part heat insulating board when the rising molten steel surface stops or approaches the stop.

CONSTITUTION: In a casting method, in which the molten steel is cast while heat-insulating by using the top part heat insulating board 2 together with the ingot case 1 and generating the heat of the top part heat insulating board 2 to the top part of the bottom-poured molten steel, the edge of the top part heat insulating board 2 is laid and set on the upper edge of the ingot case 1. Then, at this step, when the rising molten steel with pouring stops or approaches the stop, the top part heat insulating board 2 is made to progress the ignition and the burning. By this method, the development of inclusions and the fear of carburization caused by use of the heat insulating board 2 are almost eliminated.