PURPOSE: To simplify a control system, and to improve a dimension accuracy of a plate by raising a looper roll placed between stands when a strip is bitten into a lower side stand, and controlling a relative speed of the roll so that a looper tension becomes a prescribed tension.

CONSTITUTION: When a strip 4 is bitten into a lower side stand 2, between adjacent stands 1, 2, a looper roll 3c is made to contact by pressing to the strip by operating an automatic arm angle control part 10 by a signal of a rolling reduction load cell 9, and raising an arm 3b up to a prescribed angle θ by a hydraulic cylinder 3d. A load is detected by a load cell 5 of a looper 3, and a strip tension between the rolls is made constant by controlling a relative speed of a roll motor M of the upper side stand 1 by a roll speed control part 11 so that its load becomes a prescribed value. A tension of a strip is made constant, and a plate accuracy is improved by a simple control system.