Abstract: A device for controlling a speed of rolls of a rolling mill is disclosed which includes means for reducing an amount of drop of the speed of the rolls and a speed restoration time when a work to be rolled is introduced between the rolls.

Abstract: A digital control device includes a first controller which generates a control reference signal of a first controlled variable of a controlled system, a first frequency converter which converts said control reference signal into pulses of a frequency proportional to a magnitude thereof, a second frequency converter which converts a measured value of a second controlled variable of said controlled system into pulses of a frequency proportional to a magnitude thereof, and a second controller which obtains a difference between the output pulses of said first frequency converter and the output pulses of said second frequency converter and which controls said second controlled variable by using said difference as a control reference value.