Abstract: Documents are stacked on edge on a bed assembly having a backplate assembly near one end and a slidable backstop assembly aranged to be incremented away from the backplate assembly as the documents fill the stacking space therebetween. The backstop assembly is fixed to and alternately freed from the bed assembly by an escapement assembly coupled therebetween and actuated electrically. Preferably the escapement assembly comprises a pawl and ratchet together with cogged or spurred belts guiding the backstop assembly along the bed assembly. A photoresponsive, or like, assembly is arranged to sense the entrance of documents into the stacking space, and electric reed switches and corresponding actuating magnets are assembled on the backstop and bed assemblies for predetermining an initial increment of stacking space.