To fix an appropriate clamper 37 to a prescribed position after the position change in a carriage 27 by avoiding the positional deviation of the appropriate clamper 37 after the position of the appropriate clamper 37 with respect to the carriage 27 is changed.

When a cylinder body 43 having a first piston 47 and a second piston 49 is integrated with each clamper 37, and each first piston 47 is moved forward of the cylinder body 43, a corresponding first locking member 83 is moved downward by the action of a toggle link mechanism 85 to press a first fixing unit 35 in a carriage 27 from the top, the first piston 47 is moved backward of the cylinder body 43 to press a second fixing unit 95 by a second piston rod 59 from the forward side, and the corresponding second locking member 93 presses the second fixing unit 95 from the backward side.