PURPOSE: To stabilize the quality by controlling a molten metal level to the optimum by using a correction parameter based on a molten steel flow amt. gain found from an effective through hole area which is estimated from a casting speed, tundish level and casting size.

CONSTITUTION: A molten steel is cast in a mold 3 via a dipping nozzle 2 from a tundish 1 and the flow amt. thereof is adjusted by the sliding gate 5 driven by a cylinder 4. In this case, the error in the measuring value by the molten metal level gage 6 using a γ line and the set value is corrected by amending the parameter of PID arithmetic part 8a. By this method, the quality can be improved.