PURPOSE: To increase ability for correcting skews while preventing blank skewing from the center of a registering roll by reducing conveying force of a conveyer means when a blank is near the registering roll.

CONSTITUTION: When a blank 18 reaches right front of a registering roll 6, a detecting switch 17 detects the blank 18 to send a signal to a solenoid 16 which is operated by the signal to drive an arm 14 in the direction d. The arm 14 drives an idler roll 18 in the direction e. Thus, nipping force of the idler roll 18 and drive roll 12 is reduced so that the rear end of the blank 18 is prevented from loop formation when the leading end of the blank 18 abuts against the registering roll 6 and stops. Also, since the blank 18 is conveyed by a large conveying force until the blank 18 reaches the registering roll 6, any skews do not occur and the blank 18 is registered with the registering roll 6 without any skews from the center.