A device for aligning plate-like workpieces traveling in a machine direction in a machine processing them, more particularly in a folder-gluer, comprising an upper aligner and a lower aligner. The lower aligner is equipped, on the one hand with a guiding member mounted on a lower guide, and on the other hand with a lower conveyor having at least one useful portion which is fixedly attached to an upper guide movable in the horizontal plane with respect to the lower guide. The lower and upper guides form a bearing element unit, which is weakened by an opening extending between the guides.