PURPOSE: To prevent easily variation of the sheet-metal gauge of rolled materials caused by the eccentricity of the backup roll of a rolling mill, by delaying the eccentric waveform of the backup roll by one cycle and constituting a phase cycle loop so that the coefficient of correlation before and after the 1-cycle delayed eccentric waveform becomes maximum.

CONSTITUTION: Out of the signal of a rolling load cell 4 fitted to a backup roll 3 of a rolling mill, an amount equal to the change in load is calculated at a lock-on circuit 31 and only an amount equal to the roll eccentricity is fetched at a by-pass filter 32 by by-passing the change of low frequency contained in the signal due to the variation of thickness. Then the amount equal to the roll eccentricity is inputted into a phase cycle loop 30 and a completely synchronized control signal is outputted to a hydraulic rolling down control device 8 after the gain of the control signal is adjusted at a gain correcting circuit. Since the responding correction of the rolling reduction system can be made freely, the eccentricity of the backup roll 3 can be controlled with high accuracy and the variation of thickness of rolled sheets caused by the eccentricity of the backup roll can be prevented.