Abstract: An elongated carton supporting rail is mounted on a frame along with means for guiding an opened-out upright carbon blank to a predetermined position, with the edges of its bottom minor flaps resting on the rail. Flap closing elements automatically engage the bottom minor and major flaps of the carton in sequence immediately following the engagement of the carton with a switch lever when the carton is in the proper position on the rail. The minor flaps are folded above the carton supporting surface of the rail and in parallelism therewith, and the major flaps are folded below the carton supporting surface of the rail. The carton is then filled while supported on the rail, and thereafter is engaged by a pushing element and slid longitudinally off the discharge end of the rail.