PURPOSE: To separate roll arrangement for away and to fix a hydraulic pressurizing mechanism during stretching work by separating a part which is necessary to control a roll pressure from a part for moving the arrangement of a roll assembly.

CONSTITUTION: So as to easily introduce the tip of a strip, lifting devices 11, 12 are started so that the upper part 2 is moved from the position where the interval between work rolls is separated to the working position. Simultaneously an adjusting device 14 is begun to work and the upper part 2 can be lowered. After that, a pressure medium for forming a roll pressure is introduced into a cylinder space between a piston 16 and the collar 18 of a cylinder casing 17. Therefore, since the free height of the cylinder space is extremely low, even when the quantity of the pressure medium is small, the roll pressure is extremely strongly adjusted.