To restrain the variation of molten steel level in a mold with a simple control movement and the min. time of sliding of a sliding nozzle at the lower part of a ladle.

In a control system of molten steel level in a tundish, the sliding nozzle 3a at the lower part of the ladle 1 is moved with one dead zone. Further, the opening degree of the sliding nozzle 3b at the lower part of the tundish 2 to a cast drawing velocity is calculated from the cast slab drawing velocity and the molten steel level in the tundish with a nozzle opening degree calculating art 15, and this value is given to a mold level control as a feedforward quantity. By this method, even in the simple control movement, the variation of the molten, steel level in the mold can be restrained.