PURPOSE: To eliminate slip and to improve operating efficiency by detecting the slipping phenomenon basing on the output signal of a rolling reaction detector and changing the speed of a rolling roll in accordance with the signal.

CONSTITUTION: In case of generating slip during rolling, a rolling-reaction deviation signal 17 increases in the plus direction; a comparator 14b compares and discriminates the time when the signal 17 becomes larger than a slip-detection- level set signal 18 to set a slip detection signal 20, and detects it automatically. When the signal 20 turns ON, a speed changing signal corresponding to the signal 17 is outputted as a speed compensation signal by a rolling-reaction/speed- level converting circuit 22. As a result, when the speed of a rolling roll decreases and a slipping phenomenon settles down, a rolling reaction signal 10 increases and the signal 17 decreases; and a comparator 14c discriminates the time when the signal 17 becomes smaller than a slip-OFF-level set signal 19, to reset the signal 20.