Abstract: An improved stacker for an automatic document sorter is described. The stacker is vertical and receives documents at the top thereof and expels them at the bottom. The stacker includes a paddle normally disposed at the top for receiving the first document and subsequent documents stacked thereon. As documents enter the stacker, the paddle drops due to the action of a timing belt and sensor arrangement until it reaches the bottom. At the bottom, a horizontally directed timing belt withdraws the paddle from the stacker and the paddle is then returned by reverse action to the top of the stacker and reinserted thereinto for receiving the next stack of documents. Both timing belts are independently driven by motors.