PURPOSE: To decrease the fish tail produced by hot rolling and to improve yield by forming compression formed parts in the transverse direction in the top or rear end part of a slab with a vertical scale breaker thereby preforming the slab inexpensively.

CONSTITUTION: At least one of the top and rear ends of a slab S heated in a heating furnace 1 are pressed to form compression-formed parts Sc on both end parts of the slab just before edging with the vertical rolls 21 of a vertical scale breaker 2 prior to edging with said rolls and further prior to hot rolling with the edger rolls 31 and horizontal roughing rolls 32 of roughing mills 3. If the slab S preformed in such a way is subjected to ordinary broadside rolling with the vertical rolls 21, the top and rear end parts of the slab S pass through the rolls without rolling down; therefore, the growth of fish tails is small and the fish tails after the rolling is decreased condiderably.