To prevent deterioration of the ingot surface skin or entrainment of a cover material covering the molten metal surface by eliminating the inflow of a seal gas into a casting mold, and removing a large fluctuation of the molten steel surface, in an underside pouring method for a molten metal using the seal gas.

For preventing the gas entrained into the molten metal from flowing in the casting mold 7, a gas discharge path for extracting the gas is provided between a pouring tube 3 and a runner 5 connecting the tube and the casting mold 7a the closest to the tube. The casting method is constituted so that in an underside pouring ingot making method for casting the molten metal using the seal gas, a gas extracting tube 6 for extracting the gas is erected on the runner 5 between the pouring tube 3 and the casting mold 7a the closest to the tube to conduct the casting.