An assembly device for plate elements such as sheets of paper, cardboard, corrugated cardboard or similar material, for subsequent operation thereon in a processing machine. A feed station feeds elements to a positioning station for the plate elements. The positioning station for the plate elements includes a lower part equipped with first conveyors arranged side by side and an upper part including a second conveyor movable transversely with respect to the first conveyors. The second conveyor include grippers for the plate elements. The positioning station has a device for assembling the plate elements with respect to each other and an aligning device for longitudinally and transversely aligning the plate elements.