PURPOSE: To stably edge even a thin slab.

CONSTITUTION: A taper roll mill 4, flat roll mill 2 and edger 1 are aligned. By alternately feeding a slab 3 forward, backward and forward, the thickness is rolled down to widen the width through the taper roll mill 4 and the flat roll mill 2. The slab 3 is edged by the edger 1 and the width is controlled. The edging by the edger 1 is forcedly performed once or more than once if necessary.