Abstract: A carton folding apparatus operable to close the top of a carton having a front inner flap, a rear inner flap, a right outer flap, and a left outer flap. The carton folding apparatus comprises a frame which has an input end and an output end. Extending between the input end and the output end of the frame is a conveyor which is adapted to transport cartons from a position upstream of the input end of the frame to a position downstream of the output end thereof. A flap folding assembly is mounted for vertical movement along the frame in order to accommodate cartons of various sizes. The flap folding assembly is positioned above the conveyor and includes a stationary front flap folding bar, a rotatable rear flap folding arm, a right outer flap folding member, and a left outer flap folding member. Each of outer flap folding members includes an end. The ends of the outer flap folding members are adapted to be moved closer to or further from one another upon rotation of the outer flap folding members.