A gap between a bearing box and a roll portion and so on which are not used for absorbing an expansion of a roll are reduced, and by increasing axial widths of the bearing box and cylindrical roller bearing for that, a loading capacity of the cylindrical roller bearing is enhanced.A first side face 13A of the bearing box 13 located at one side in the axial direction is disposed outwardly with respect to a central line Y2 between two roll portions 22A, 22B than a second side face 13B located at an other side in the axial direction, and a gap a1 between this first side face 13A and the roll portion 22A opposed thereto is made smaller than a gap a2 between the second side face 13B and the roll portion 22B opposed thereto.