PURPOSE: To always stably hold level of molten metal in a mold to the suitable position by using fuzzy inference, in which various factors are made to membership function and correcting opening degree of a nozzle for pouring molten metal.

CONSTITUTION: At the time of drawing as a continuous cast slab 4 by pouring the molten steel in a tundish 1 into the mold 3 for continuous casting from the nozzle 2, a membership function storing part 10 for storing the membership function 10b, in which assumes relation between casting velocity detected value from a casting velocity detector 8 and variable quantity of the molten steel level in the mold 3, the membership 10a, in which regulates relation between tundish wt. detected value from tundish wt. detector 9 and molten steel discharging rate, and the membership 10c, in which regulates variation of the molten steel discharging rate caused by a nozzle 2 as the time function, respectively, is arranged. The correcting value based on the above memberships 10a-10c is inputted to the fuzzy inference part 11 and the correcting value D to the nozzle opening degree control value D outputted to a level controller 7 is obtd. and by this, the opening degree of nozzle opening/shutting device 6 is adjusted to always hold the molten steel surface level in the mold 3 to the fixed height.