Abstract: When the number of pieces of postal matter stacked at a stacking section in a sorter with an automatic push-out apparatus of the invention reaches a number which allows a push-out operation before or after a full-stack operation, the postal matter is transferred to a corresponding empty tray. The postal matter which is to be stacked at this stacking section during the push-out operation is stacked at a preliminary stacking section. After the stacking section is restored, the postal matter stacked at the preliminary stacking section is transferred to the empty tray.