PURPOSE: To obtain the flatness of a rolled plate on the outlet side within an allowable flatness by setting an initial condition of a shape controlling actuator based on the target crown ratio and correcting the initial set condition to a condition having an allowable flatness when an actual flatness is over the predicted flatness.

CONSTITUTION: After the initial condition of shape correcting actuators for upper and lower work roll bending devices 5 and 6 and the like is set based on the target crown ratio, for instance, an outlet side extending difference ratio is found from a flatness model. The flatness is decided whether within or out of the preliminarily set allowable flatness and an outlet side plate crown by which the flatness obtained based on the flatness model is within the allowable flatness is used as the outlet side target plate crown to correct the condition of the shape controlling actuator when the actual flatness is out of the allowable flatness. Thus, the outlet side flatness is surely within the allowable flatness and the rolled plate having a excellent shape is obtained.