PURPOSE: To obtain a clamping device which is small-sized and has good mechanical strength and accuracy by connecting an inlet side clamp and an outlet side clamp and providing a clamping mechanism for cross adjustment separately from the inlet side clamp.

CONSTITUTION: A preceding plate 6 and a succeeding plate 5 are clamped by an inlet side clamp 1 and an outlet side clamp 2. The clamped plate 6 and plate 5 are cut parallel by a shear, then the clamp 1 moves by a specified distance toward the clamp 2. Since the clamp 1 and the clamp 2 are connected on both sides by chucking mechanisms 9, 9 and therefore the clamping device has high strength and mechanical accuracy. On the other hand, if there is a deviation in the transverse direction of the plate 6 and the plate 5, the clamp 8 is moved in the transverse direction of the clamp 8 by a cross adjusting cylinder 4 attached to a cross adjusting clamp 8 provided separately from the clamp 8, by which the deviation is corrected.