PURPOSE: To prevent generation of metallurigical and shape defects such as double surfaces, cracks and the like by forming a molten steel well between a pair or water-cooled rolls and a tundish, and casting the molten steel while acting the static pressure of the molten steel in the tundish.

CONSTITUTION: An oil hydraulic cylinder 8 operates to open the nozzle part of a slide gate valve 7, through which the molten steel in a tundish 1 is charged into a molten steel dam 3. The static pressure of the molten steel level in the tundish 1 acts upon the surfaces of a pair of water-cooled rolls 2, 2' and the solidified shells 17 formed on the surfaces of the rolls 2, 2' are pressed and adhered tightly to the surfaces of the rolls 2, 2' by the static pressure at all times during casting so that such restraining forces by which the parting of shell 17 from the surfaces of the rolls 2, 2' is prohibited, are given to said shells 17 on account of thermal shrinkage. Therefore, the shells 17 are adhered tightly to the surfaces of the rolls 2, 2' without producing any air gap and are uniformly cooled, whereby the generation of metallurgical and shape defects in a product 18 is obviated.