PROBLEM TO BE SOLVED: To enable the supplying of molten metal under perfectly closing condi tion and to improve the workability by arranging a degassing treatment appara tus, in which inert gas is fed into the molten metal through a supplying course of the molten metal from a storing vessel to enable bubbling. SOLUTION: At the same time of the degassing treatment of the molten metal 36, this molten metal 36 is fed into the storing vessel 12 and can be supplied from the storing vessel 12 to a fixed quantity vessel 22. When the molten metal 36 fills up into the fixed quantity vessel 22, a valve 18 is closed and a valve 26 is opened and the inert gas is fed into the inner part of the fixed quantity vessel 22 from a pressing passage 24 to pressurize the inner part of this fixed quantity vessel 22. The molten metal 36 in the fixed quantity vessel 22 is supplied into an injection sleeve through the molten metal supplying passage 28 by this pressure. In such a way, since while continuously executing the degassing treatment to the molten metal 36, the molten metal 36 after the treatment can be supplied, the deterioration of the molten metal 36 caused by the contact with the air can be prevented, and the workability is improved.