PURPOSE: To symmetrize the roll bending of work roll and to flatten the shape of steel strip by applying the bending pressure of upper and lower work rolls symmetrically in relation to the center of rolling mill.

CONSTITUTION: Oil pressure is applied on one end side of the upper work roll 1 and the other end side of the lower work roll 2 with a piping 8a through a servovalve 7a from a hydraulic source 6. And, oil pressure is applied on the other side of the upper work roll 1 and one end side of the work roll 2 with a piping 8b through a servovalve 7b. The bending curve of the work rolls 1, 2 at the time of rolling can be always controlled in line symmetry in relation to the center line of the rolling mill by applying the bending pressure of the same hydraulic force in point symmetric positions of the rolled stock 3 with two systems of the servovalves 7a, 7b in the above-mentioned manner.