PURPOSE: To suppress the growth of a solidified shell and to maintain the specified meniscus by using a refractories having poor wettability and high bending strength to constitute the lower part of the gate refractory board on the front face of a gate body and dividing the gate refractory board to a plurality in the transverse direction of a casting mold.

CONSTITUTION: The gate refractory board 6 is attached to the front face of the gate body 4 of a gate 2 which partitions the inside of the casting mold. The gate refractory board 6A to be formed with the solidified shell in the lower part of the board 6 is constituted of the refractories such as silicon nitride having the poor wettability and high bending strength. The upper gate refractory board 6B is constituted of molten silica, etc. having relatively high strength. Then the solidified shell formed from the gate refractory board 6 peels therefrom at the point of the time when said shell grows to some extent and the meniscus is thus stabilized. The defect on the base side of the slab is therefore eliminated. The gate refractory board 6 is divided to a plurality in the transverse direction of the casting mold. The stress to be exerted to the board 6 is thereby relieved when external force is exerted to the refractories.