PURPOSE: To increase the yield of a product by setting the number of revolutions of a mill motor at steady operation time at the reference value and by multiplying each reference value by common constant, then by commanding the number of revolutions of each mill motor based on this calculated value.

CONSTITUTION: Pulse generator PL1, PL2...PLn are provided respectively for each mill motor M1WMn of the 1stWnth stand S1WSn and an arithmetic and control circuit 10 is arranged as well. The number of revolutions at the normal driving time prior to emergency stop is stored by taking the number of revolutions of each mill motor M1WMn from each pulse generator PL1WPLn into the arithmetic and control unit 10. At the time of reactuating, the control of the number of revolutions is performed by outputting to each mill motor M1WMn the product multiplying by the coefficient determined by time, by making the stored number of revolutions as the reference. In this way, the conformity of the number of revolutions of mill motor is secured with each other, the generation of a product flaw is reduced and the product yield is increased.