PURPOSE: To maintain the specified horizontal deflection positions of work rolls by bringing the work rolls into pressurized contact with each other by a prescribed pressure, pressing horizontal side support rolls to the work rolls by the force corresponding to the horizontal component of force thereof and thereby adjusting the zero point position.

CONSTITUTION: The work rolls 2a, 2b are previously brought into pressurized contact with each other by the predetermined pressure P. The force F corresponding to the horizontal component of force thereof is applied by a hydraulic cylinder 35a to the horizontal support roll 7a and the horizontal intermediate roll 6a to push back to the work roll 2a so that the axial line thereof is returned to a straight line. A hydraulic motor 75a is driven to lower a wedge 29a until the wedge comes into contact with a supporting member 24a. The contact is detected by the increase of the detection oil pressure of an oil pressure gage 76a and the hydraulic motor 75a is stopped. The gap between the rolls is eliminated in this way and the horizontal bending of the work roll 2a is eliminated. The hydraulic cylinder 35a is actuated to pressurize the supporting member 24a to the wedge 29a side. The same operation is carried out on the (b) side as well fo complete the zero point adjustment.