To effectively prevent the development of surface oxidation in a mold, at the time of reusing a tundish in a hot state.

Into the tundish 16 remained-sticking metal 12 after completing continuous casting, molten metal 11 set to the higher overheating degree than the molten temp. of the molten steel 11 in the tundish 16 is poured through a long nozzle 15 in a molten steel vessel 13 for holding the molten steel 11. The molten steel 11 in the tundish 16 lowering the temp. by contacting with the metal 12 is poured into the mold 20 for continuous casting through an immersion nozzle 18 arranged at the lower part of the tundish 16. At this time, exothermic powder layer is formed on the molten steel surface in the mold 20 for continuous casting. Further, the exothermic powder uses the powder having 900-2000kcal/kg calorific value.