PURPOSE: To prevent the generation of camber by calculating the quantity of camber basing on the detecting values of sheet width-end detectors provided to the front and back of a mill and calculating successively the correcting quantity of leveling so as to make the quantity of camber to be zero.

CONSTITUTION: Sheet width-end detectors 3, 4 are provided to the front and back of a mill 1 to detect the sheet width W and the distance X at the provided positions. When the detecting value of detector 3 is inputted to a shift counter 6; it is transferred, synchronously with the material-feeding length obtained from the output pulse of a pulse oscillator 5 used for detecting the number of revolutions of a roll, to the spot just below the mill 1. An arithmetic device 7 calculates the quantity C of camber just below the mill 1 basing on the detected value Cc of detector 4 and the detected value of shift counter 6. An arithmetic device 8 calculates the correcting quantity of leveling basing on said value C, to input it to rolling-reduction controlling devices 9, 10. By this method, the generation of camber is prevented, and the yield in rolling process is improved.