PURPOSE: To obtain a cast slab having good surface without any leakage of molten and to reduce comsumption of slag by giving number of oscillation to a mold in proportion with casting speed in low speed range at the time of casting start and stop, and giving the constant number of oscillation having short negative time in the aimed speed range.

CONSTITUTION: The oscillation is given to the mold in the continuous casting and artificial slag is enclosed at suitable quantity between the mold and devel oped shell, to make cast slab surface having shallow oscillation mark. In case of enlarging the number of oscillation to the constant casting speed, the consump tion of slag is reduced, and also in case of enlarging the casting speed, the consumption of slag is reduced. Therefore, in the low speed range at the times of casting start and stop, the number of oscillation to the mold is given in proportion to the casting speed, to prevent seizure caused by little quantity of slags. In the intermediate aimed speed range, the constant number of oscilla tion having short negative time is given to enclosure slag suitably and obtain the cast slag having good surface without any leakage of molten metal. There fore, the consumption of artificial slag is suitable.