PURPOSE: To improve response speed and to drastically reduce the variation of molten metal surface by estimating the response delay in a molten metal surface level control device based on the moving delay in a machine part and recovering with correction.

CONSTITUTION: By the molten metal surface level control means, opening degree of a gate plate 6a in a sliding nozzle 6 arranged on the way of an immersion nozzle 4 for supplying the molten metal 3 into a mold M from a tundish T is adjusted while comparing the measured value by a level detector 9. The gate plate 6a in the sliding nozzle 6 is opened/closed by a stepping cylinder 7, and the cylinder 7 is driven by a pulse motor 8. The delay is developed in between spool movement by the pulse motor 8 and cylinder rod movement of the stepping cylinder, and by this method, the molten metal pouring quantity is varied. From the moving characteristic of the cylinder rod, etc., this variable quantity is estimated and corrected by an arithmetic control part.