PURPOSE: To improve the formation of the finer grains in solidifed structure and the central segregation of a billet arising from such formation by blowing deeply iron powder into the crater of the billet by a carrier gas blown through lances which are depply inserted to the inside of the region enclosed by a continuous casting mold.

CONSTITUTION: Plural pieces of the blowing lances 6 are deeply inserted into the casting mold 1. The iron power entrained in the carrier gas selected from inert gases such as Ar and N2 according to the steel kind is fed to the lances 6, by which the blowing is started. Casting is thereafter started by opening the sliding nozzle of a tundish. The lances 6 are lowered down to the prescribed depth, for example, near the crater end in synchronization with the casting and the blowing of the powder 7 is continued.