Abstract: The device has a rotating member including pulleys that and joined to a belt conveyor along which flat folded cases advance. Suction cups are mounted on shafts situated along the periphery of the rotary member and a coaxial drum, rotating in synchrony with the pulleys, carries the shafts which are made to oscillate by crank means. The drum also supports rocking levers which are in engagement with a cam and cause cranks to rotate. Further suction cups, situated at the outlet of the feeding line, are moved in phase relation with the previous suction cups between a gripping position, in which the suction cups grip a flat folded case on opposite sides, and a position in which adjacent wall panels of the case are opened. Belt conveyors receive the opened case and trail it along a packaging line.