PURPOSE: To prevent the development of product defect by arranging a solid metal in a mold and a flat separating wall following to change of molten metal surface and next executing the casting.

CONSTITUTION: The solid metal 2 is charged or hung down in the mold 1 and the float separating wall 3 is arranged at the outer circumference, so as to be possible to follow the change of molten metal surface 4. The float separating wall 3 is composed of refractory, such as alumina, etc., and the dimension is decided, so as to submerge under the molten metal surface 4 at the lower end thereof during casting and expose above the covering slag 6 surface at the upper end thereof. Therefore, the separating wall 3 is shifted as following to the change of molten metal surface 4, based on the shape and specific gravity of separating wall 3. In this way, while the solid metal 2 is brought into contact with molten metal under clean condition during casting, the solidification is progressed. Therefore, the development of product defect is prevented.