Abstract: An apparatus for receiving sheets traveling seriatem along a path, and accumulating such sheets in a stack justified along one marginal edge thereof. The apparatus includes a tray into which sheets are directed, one after another, from the sheet travel path for accumulating such sheets into a stack on the tray. A striker plate is associated with one marginal edge of the tray. The accumulated sheets are continuously urged into engagement with the striker plate to justify one margin of the accumulated sheet stack. The mechanism for urging the sheets into engagement with the striker plate is supported relative to the striker plate on the opposite side from the sheet travel path and extending over the tray, and under the influence of gravitational forces follows the level of the topmost sheet in the stack.