Method for processing a blank intended to form, after folding-gluing, a folded flattened box, the method comprising the following steps: a) supplying a substantially flat blank comprising a right-hand edge, a left-hand edge, a front edge, a rear edge, a right-hand longitudinal crease and a left-hand longitudinal crease, the right-hand longitudinal crease and the left-hand longitudinal crease delimiting, with the right-hand edge and the left-hand edge at least three flaps including a right-hand flap, a left-hand flap, and a central flap, b) applying glue in an area of the right-hand flap adjacent to the right-hand edge and/or in an area of the left-hand flap adjacent to the left-hand edge, such that the glue is present in an overlapping portion between the right-hand flap and the left-hand flap, c) folding the right-hand flap 180° around the right-hand longitudinal crease towards the central flap, and folding the left-hand flap 180° around the left-hand longitudinal crease towards the central flap, d) closing the folded right-hand flap and the folded left-hand flap which are located one above the other at least in the overlapping portion, e) checking by optical detection the position of the right-hand edge and the left-hand edge and comparing this effective position with a predetermined position so as to determine any positional deviation, f) when the positional deviation exceeds a permissible deviation value, carrying out the following sub-steps before the glue sets: f1) blocking the central flap by its bottom surface using blocking means, operating with vacuum depression of the bottom surface, and comprising at least one ramp equipped with nozzles directed upwards and able to create a vacuum, and then f2) holding the top surface of the folded right-hand flap and the folded left-hand flap and f3) correcting the position of the left-hand flap and/or the right-hand flap, g) applying pressure between the right-hand flap and the left-hand flap in the overlapping portion until the glue sets, and h) releasing the central flap, the right-hand flap and the left-hand flap. a) supplying a substantially flat blank comprising a right-hand edge, a left-hand edge, a front edge, a rear edge, a right-hand longitudinal crease and a left-hand longitudinal crease, the right-hand longitudinal crease and the left-hand longitudinal crease delimiting, with the right-hand edge and the left-hand edge at least three flaps including a right-hand flap, a left-hand flap, and a central flap, b) applying glue in an area of the right-hand flap adjacent to the right-hand edge and/or in an area of the left-hand flap adjacent to the left-hand edge, such that the glue is present in an overlapping portion between the right-hand flap and the left-hand flap, c) folding the right-hand flap 180° around the right-hand longitudinal crease towards the central flap, and folding the left-hand flap 180° around the left-hand longitudinal crease towards the central flap, d) closing the folded right-hand flap and the folded left-hand flap which are located one above the other at least in the overlapping portion, e) checking by optical detection the position of the right-hand edge and the left-hand edge and comparing this effective position with a predetermined position so as to determine any positional deviation, f) when the positional deviation exceeds a permissible deviation value, carrying out the following sub-steps before the glue sets: f1) blocking the central flap by its bottom surface using blocking means, operating with vacuum depression of the bottom surface, and comprising at least one ramp equipped with nozzles directed upwards and able to create a vacuum, and then f2) holding the top surface of the folded right-hand flap and the folded left-hand flap and f3) correcting the position of the left-hand flap and/or the right-hand flap, f1) blocking the central flap by its bottom surface using blocking means, operating with vacuum depression of the bottom surface, and comprising at least one ramp equipped with nozzles directed upwards and able to create a vacuum, and then f2) holding the top surface of the folded right-hand flap and the folded left-hand flap and f3) correcting the position of the left-hand flap and/or the right-hand flap, g) applying pressure between the right-hand flap and the left-hand flap in the overlapping portion until the glue sets, and h) releasing the central flap, the right-hand flap and the left-hand flap.