PURPOSE: To prevent penetration of molten metal into a hot-top forming material and to make a casting surface of an ingot smoothly by arranging a graphite sheet layer on the surface of a fire resistance insulating material brought into contact with the molten metal in the hot-top forming material.

CONSTITUTION: At the upper part of an ingot case 6 laid on the bottom plate 5, the hot-top forming material 1 having a tapered part at the lower part as widening underward, is formed under assembling. The graphite sheet 3 is laid as a piece at contacting surface with the molten metal for the fire resistance insulating material 2 as the main body of the hot-top forming material 1 and along the non-contacting part with the molten metal at the back side of the tapered part. By this graphite sheet 3, the penetration of the molten metal into the fire resistance insulating material 2 is prevented and therefore, the ingot having smooth casting surface is obtd. A partial of the graphite sheet 3 is burnt down, but remaining graphite sheet 3, which is not burnt, is easily removed together with the fire resistance insulating material 2 after casting.