Apparatus is disclosed for stacking bundles such as bundles of paperboard sheets on a receiver. The apparatus includes an L-shaped conveyor having a top run and a bottom run. The top run of the conveyor has a position defined by the location of spaced first and second carriers having discrete guide members contacting the conveyor. The carriers are individually elevated with the second carrier being progressively elevated in stages while the first carrier moves up and down from a receiving position to a position corresponding to the current position of the second carrier.