PURPOSE: To achieve easily a center-shift performance of an article in such way that centering guarders, which are able to touch with or detouch from both sides of an article, are moved simultaneously by a single driving device.

CONSTITUTION: Guarders 2, 3 provided for the center-shift of an article 1 are respectively supported by rack bars 4, 5, which have their respective rack 10, 10 and are adapted to move at the same stroke each other via a pinion 9. The pinion 9 is driven by a motor through a reduction gear. To first adjust the position of the guarder 3, a rod 12, which supports the guarder 3 via a pin 6, is moved along the rack bar 5. Consequently, a subsequent center-shift of the article can be achieved precisely and, furthermore, easily by the rack 10 and pinion 9.