PURPOSE: To move a roll by comparatively small operating force, by placing a ball-and-roller bearing between an axle box of a moving roll and an axle box supporting surface of a housing.

CONSTITUTION: To the lateral part of the left side of a housing 1 constituting a body supporting frame by a pair of the left and right ones, an electrically- driven type or manual handle type driving device 10 for adjusting a roll gap is installed. A screw-down female screw 2 and a screw down male screw 3 connected to said device is installed to the inside lateral part of the housing 1. The tip part of the screw 3 is connected to an axle box 6 of a moving roll 4. The axle box 6 is supported by an axle box supporting surface 11 of the housing, and a ball-and-roller bearing 8 is installed to the lower surface of the axle 6. In the adjacent part of the axle box 6, an axle box 7 of a fixed roll is fixed to the housing 1, and between the axle boxes 6, 7, a preload device of a prop- up system is installed. When the device 10 is operated, the screw 3 moves forward and backward, and the axle box 6 moves on the surface 11 by rolling friction, therefore, a gap of the rolls 4, 5 can be adjusted.