PURPOSE: To easily prevent the surface crack of slab by limiting the rolling reduction of a 1st pass at the time of rough rolling based on Mn/S and the temp. of slab.

CONSTITUTION: In the rough rolling process of a hot rolling line, in the case a slab which is bloomed or continuously cast is rolled by direct rolling or after reheating, the rolling reduction of a 1st pass is limited not more than the limit draft of the generation of surface crack that is determined from the Mn/S and temp. of slab. In this way, surface crack can be comparatively easily prevented as an existing equipment is.