PURPOSE: To improve the sheet-thickness accuracy and yield of a product by alloting the high frequency region of a control input-deviation signal to a feed- forward control system, the intermediate frequency region of said signal to a mass-flow control system, and the low frequency region to a monitor control system, in performing rolling reduction.

CONSTITUTION: A measured value 10 of inlet-side sheet thickness, as an input deviation signal, is made to correspond only to a high frequency signal by a feed-forward system 14 consisting of a high-pass filter 11 and a timing controller 12, etc., and is inputted to an adder 15. Next, the value 10 is inputted to the adder 15, together with an inlet-side sheet speed 16 and an outlet-side sheet speed 17, through an outlet-side sheet-thickness estimator 18, a filter 20, and a controller 13-2, while corresponding only to an intermediate frequency signal. In the same way, a measured value 22 of outlet-side sheet thickness is inputted to the adder 15 while corresponding only to a low frequency signal; then the sheet thickness is simply controlled so as to flatten the gain characteristics ranging from high frequency to low one by adjusting the gains of individual controllers 13-1, 13-2, etc. of said three control systems.