A carton loading machine has an endless carton conveyor which extends in a horizontal path which in plan view extends in a generally square configuration. A plurality of carton receptacles are mounted on the endless conveyor for movement therewith. Retainer bars are arranged opposite the open ends of the receptacles along at least three sides of the square configuration of the path and these retainer bars are mounted for simultaneous movement with respect to the receptacles so that the space between the retainer bar and the oppositely disposed wall of the receptacle can be adjusted to accommodate articles of different sizes. A further retainer bar is located below the open lower end of the receptacles and extends along at least two sides of the square configuration of the conveyor path. These second retainer bars are also simultaneously adjustable in height with respect to the receptacles so as to accommodate cartons of different length in the receptacles.