PURPOSE: To surely and easily open or close a passage for molten metal by using a metallic shielding member contg. a cooler in the passage for the molten metal flowing out of a metal refining furnace.

CONSTITUTION: Molten metal M flowing out of a refining furnace flows into troughs 3 and 3 from a trough 1 through a branch trough 2. When the molten metal M flowing in one trough 3 is blocked, a metallic shielding member 5 contg. a cooling water passage 5a and connected to a cooling water supply pipe 7a and a cooling water discharge pipe 7b is inserted into the trough 3 and cooled by cooling water. Consequently, the molten metal flowing in the trough 3 is blocked without melting the member 5. When molten metal is allowed to flow in this trough 3, the pipes 7a and 7b of the member 5 are detached, cooling of the member 5 is suspended, hence the member 5 is melted off by the temp. of the molten metal, and the molten metal easily flows down in the trough 3.