PURPOSE: To reduce the amount of crop and to improve the yield of rolling by recognizing the shapes of the front and rear ends of a rolling material before and after the rolling of vertical rolls and controlling the vertical rolls.

CONSTITUTION: In a reversible mill equipped with vertical rolls 2, recognition devices 3, 4 of crop-shaped pattern are provided to the front and rear sides of the vertical rolls. The devices 3, 4 determine the outside shape of crop by removing noise after taking the photograph of the outside shapes of crops at the front and rear ends of a rolling material 5 and quantifying them. A vertical roll-gap controller 10 controls the vertical roll gap basing on the outside shapes of crops to reduce the cut out quantity of the crops.