This is a method and device for making a packaging box from two blanks (2, 3), wherein blanks are taken simultaneously from two adjacent stacks (25, 26) and placed on two parallel tracks (29, 30), the blanks are transferred flat until butted longitudinally to an assembly station, the first blank is glued on its way to the longitudinal abutment position, the first and second blanks are butted laterally into their respective positions to give them an exact lateral reference position, they are grasped, and transferred laterally, and the second blank is placed on the first blank which is thus indexed, escaping the drivers (61) of the first track (29) when the second blank is placed against the fast blank, but clamped by vertical pressure. The second blank is then applied to the first blank to glue them together in their respective defined longitudinal positions, and the resulting set of blanks is then transferred to an erecting station where the box is erected by rolling the blanks around a core.