PURPOSE: To cast economically and continuously a thin slab having good quality by controllig the width of feed flow and molten steel pool with the electromagnetic force generated by induction coils disposed oppositely on the side face of the feed flow to a continuous casting machine.

CONSTITUTION: The molten steel supplied from a tundish 1 is introduced with a feed device 2 into a molten steel pool 9. Induction coils 8 are disposed oppositely in one or ≥2 stages on the side face of the feed flow, and when the electromagnetic level of the coils 8 is successively increased, the width W1 of the feed flow and the width W2 of the molten steel pool can be narrowed. The molten steel flow part where a solidified shell is not yet formed can be thus flowed in the state of detaching the same from a dam block 5. Therefore, any block 5 is usable as far as the same supports and guides the slab, and the surface quality of the slab is thus remarkably improved.