A folding box gluing machine contains one upper and lower transport belt disposed on each side of the machine. A lower transport belt is guided in a roller cheek and an upper transport belt is guided in a roller rail. A central roller cheek and a central roller rail, which can be fed in, are further disposed in the center of the machine and in each case guide a central transport belt. A device for inserting side parts of a folding box blank, which side parts overlap and/or engage in one another, is provided. The device is fastened to the central roller rail and is driven by the central upper transport belt through a V-shaped belt. The device for inserting is held on a holding frame in a load bearing frame which can be fed in separately. The central roller rail is additionally fastened to the holding frame.