PURPOSE: To quickly stabilize casting velocity and to continue the stable condition in high accuracy.

CONSTITUTION: Until the casting velocity of a cast slab by a twin roll type continuous caster 1 stabilizes, a tundish wt. preset value preset with a tundish wt. setter 6a is inputted to a tundish wt. adjuster 6 outputting a tundish wt. adjusting signal to a hydraulic servo 7, and the tundish wt. adjusting signal based on the difference between the preset value and the tundish wt. detected by a load cell L is outputted. After the casting velocity stabilizes, by arranging a casting velocity adjuster 8 outputted after PIO-operating the pressure difference between the aimed casting velocity V and the detected actual casting velocity (v) with a motor revolutional detector 5a for driving the twin roll type continuous caster 1, the casting velocity can quickly be stabilized since the casting start at early time and further, as the molten steel is poured into the twin roll type continuous caster 1 from the tundish 2 based on the casting velocity, the stable casting velocity can be kept.