PURPOSE: To improve the stability of a molten metal surface level control in a mold with a mold molten metal surface controller in a continuous casting device, to improve the quality of a cast slab, to reduce the number of times of working in an actuator for control and to reduce power consumption.

CONSTITUTION: By adjusting a molten metal pouring quantity into the mold with the mold molten metal surface controller from the calculation of fuzzy theory based on difference between the aimed molten metal surface and the measured molten metal surface in the mold, the molten metal surface is controlled. Further, by adjusting the molten metal pouring quantity and discharging quantity with the mold molten metal surface controller in the above mold from the calculation of fuzzy theory based on the difference between the aimed molten metal surface and the measured molten metal surface and changing ratio of the casing speed, the molten metal surface is controlled.