PURPOSE: To provide a small reducing device which permits effective bus line adjustment and AGL with the reduction screw screwed into a recess of a ram housed in a cylinder in such a manner as to rotate through a worm wheel.

CONSTITUTION: A ram 2 is housed in a cylinder and a screwed shaft 5 is connected to the inner end of a reduction screw screwed into a recess of the ram. Then, the ram 2 moves in and out with the rotation of a worm wheel 7. In the adjustment of the bus line, the reduction screw is made to move in and out through rotatin of the worm wheel. At this point, the load applied on the reduction screw 1 is lessened to a small value only confined to the tars of the work roll assembly and the lower backup roll assembly. AGL is achieved by simply by feeding pressure oil between the ram 2 and the cylinder 3. With such a mechanism, a small, inexpensive equipment is made available with a sufficient responsiveness.