PURPOSE: To prevent the outflow of molten slag together with molten steel through a nozzle in the stage of charging the molten steel into a tundish through the nozzle from a ladle by floating a refractory float which injects an inert gas into the molten metal right above the nozzle.

CONSTITUTION: In the stage of charging the molten steel 2 in a ladle 1 into tundish 6 in the lower part with a nozzle 4 in the bottom part, a float 5 having the specific gravity which is the intermediate of molten slag 3 and the molten steel 2 and made of refractories provided with a porous plug at the leading end is floated freely vertically movably with a suspension rope 10 in the steel 2 and the slag 3 in the part right above the nozzle 4. In the stage of flowing down the steel 2 through the nozzle 4, an inert gas is injected through the porous plug at the leading end of the float 5. The suction of the molten slag 3 together with the molten steel 2 in the state of vortexes into the nozzle 4 is prevented by the bubbling of the inert gas, whereby the molten steel in the ladle 1 is charged into the tundish 6 in high yields without carrying the molten slag 3.