To efficiently perform the leveling work of a band saw by providing a distortion suppressing device for suppressing the distortion of a band saw having a means for parallel-moving an upper roll and/or a lower roll longitudinally in the advancing direction of the band saw.

An approach angle regulating screw 7 for parallel-moving a lower roll case longitudinally in the advancing direction of a band saw 14 by screwing motion is provided between a frame and the lower roll case 5, and when the screw 7 is rotated counterclockwise, for example, the lower roll case 5 is parallel moved backward in the advancing direction. When it is reverse rotated clockwise, the lower roll case 5 is parallel moved forward in the advancing direction. When a band saw 14 has an upward distortion, the regulating screw 7 is screwed according to the distortion to move a lower roll 6 to the left, and the approach angle of the band saw 14 is regulated upward so as to generate a distortion on the lower side, whereby the mutual distortions are canceled.