PURPOSE: To provide a small-sized straightening device with a high precision of flatness by driving endless tracks with sprockets to engage to each straightening roll and frictionally rotating each roll with supporting plates arranged inside these endless tracks.

CONSTITUTION: Respective both ends of plural straightening rolls 14 are held freely rotatable with chains 15, 16 so as to constitute track wheels 17, 18. These track wheels 17, 18 are driven with sprockets 10, 13 having teeth to engage to each straightening roll 14, and together supporting plates 19, 20 arranged inside the tracks drive each straightening roll frictionally. By uniformly and reversely rotating one side sprocket among a pair of endless tracks being deviated in half pitch against the other sprocket, the corresponding straightening rolls are rotated frictionally in hound's-tooth like on the supporting plates, so a material to be worked passed between them is orderly bent and the bent or the strain of the material can be straightened.