Abstract: A machine for folding the top flaps on a succession of boxes which are advanced on a conveyor belt. A shaft extends across the path of the boxes and has arms journaled on it for rotating and folding the trailing end flap of each box when the shaft is rotated. Torsion springs have one of their ends fastened to the shaft and another of their ends in driving contact relationship with the respective arms. When a box is in a position for one of its end flaps to be folded, limit switches are actuated in succession to cause an electrically operated clutch to turn the shaft one revolution so the arms swing around under the driving influence of the torsion springs and fold and hold the trailing top end flap until the box is advanced to the position where its end flaps are finally restrained by folding and holding its side flaps.