PURPOSE: To control pouring molten steel quantity in constant by providing a control means for controlling ascent/descent of a tundish so that distance between a molten steel level detected with a detector and the preset molten steel level in a mold becomes the prescribed distance.

CONSTITUTION: In control part 21, the distance between the molten steel level in the mold and the molten steel level in the tundish is beforehand set as the preset distance, and the control part 21 obtains the deviation between this preset distance and the calculated distance L, and a lifting device 22 is driven and controlled according to this deviation. By this method, the pouring molten steel quantity into the mold is always kept in constant and stably controlled.