PURPOSE: To prevent the development of infiltration of air into a molten metal at the time of supplying the molten metal in a tundish for continuous casting into a mold for continuous casting while controlling a flow rate with a sliding nozzle.

CONSTITUTION: At the time of supplying the molten metal flowing out from a molten metal flowing-out hole 20 provided on the bottom part of the tundish for continuous casting into the mold for continuous casting while controlling the flow rate with the sliding nozzle 8 provided on the above-mentioned molten metal flowing-out hole 2a, the sliding nozzle 8 is surrounded with a sealing box 13 and surroundings of the sliding nozzle 8 are made to unoxidizing atmosphere to execute flow rate control of the molten metal.