PURPOSE: To obtain a sufficient bending force in a narrow space by specifying the length of a fillet part and the installation in the device pressing the fillet part projecting sideways at both sides of the upper and lower separate bearing boxes at the end of upper and lower work rolls.

CONSTITUTION: Upper and lower work rolls 1, 2 are supported by upper and lower work roll bearing boxes 3, 4 respectively. At both sides of the bearing box 3 a fillet part 5 and a fillet part 6 at both sides of a bearing box 4 are provided by shortening the length thereof respectively than the length in the roll axial direction of the bearing boxes 3, 4 and in zigzags (at the left front and right back in bearing box 3 and at right front and left back in bearing box 4). The fillet part 5 is formed at some lower side position than the bottom face of the bearing box 3 and the fillet part 6 at some upper side position than the upper face of the bearing box 4 respectively and when the bearing boxes 3, 4 are superposed, the fillet parts 5, 6 are made to come within about the same horizontal plane. the fillet parts 5, 6 are then pressed by a bending cylinder.