PURPOSE: To prevent quality of a product such as rupture of a rolled stock and gage change from being deteriorated and to improve the responsiveness of the speed reference value of a mill by providing an acceleration reference arithmetic means and a speed reference arithmetic means to calculate a speed reference value from a 1st acceleration reference and a preset speed target value.

CONSTITUTION: An (n) stage differential value (n: natural number, n=n, n-1,...,1)an+1r of an acceleration calculated from the speed of rotation of a driving motor 2a to drive a mill 2 and a preset n-th acceleration target value anr are inputted to calculate the n-th acceleration reference value an. Then, this n-th acceleration reference value an and the preset (n-1)th acceleration target value an-1r are inputted to calculate the (n-1)th acceleration reference value an-1. This speed reference arithmetic unit is, provided with acceleration reference arithmetic means 61-6n to successively carry out similar calculation and require finally the 1st acceleration reference value a1, a speed reference arithmetic means 7 to calculate a speed reference value V from the 1st acceleration reference value a1 and the preset speed target value Vr.