necessary during casting so that the molten metal surface is kept constant as a matter of course the molten metal m 1 may be other metal or an alloy than aluminum the inner shape defining members 102 a and the outer shape defining member 102 b are made of for example ceramics or stainless steel and arranged near the molten metal surface in the example shown in fig1 four inner shape defining members 102 a and one outer shape defining member 102 b are arranged so as to be in contact with the molten metal surface however the inner shape defining members 102 a and the outer shape defining member 102 b may be arranged so that main surfaces of the inner shape defining members 102 a and the outer shape defining member 102 b on lower sides a molten metal surface side do not come into contact with the molten metal surface to be specific a predetermined gap of for example approximately 0 5 mm may be provided between the molten metal surface and the main surfaces of the inner shape defining members 102 a and the outer shape defining member 102 b on the lower side the four inner shape defining members 102 a define an inner shape of a casting m 3 to be cast and the outer shape defining member 102 b defines an outer shape of the casting m 3 to be cast fig2 is a planar view of the inner shape defining members 102 a and the outer shape defining member 102 b the sectional view of the inner shape defining members 102.