There is provided a base machine including a base machine feed path that conveys a paper sheet, and a validator identifying the paper sheet conveyed by the base machine feed path; an expansion unit including an extension feed path extending from the base machine feed path, a branching feed path branching from the extension feed path, and a plurality of stacking portions that are connected to the branching feed path and stack the paper sheet identified by the validator; and a control portion that, when a conveyance abnormality occur, continues conveyance operation of at least one of the extension feed path and the branching feed path without immediately stopping the conveyance operation and conveys the paper sheet to a predetermined stacking portion that is any of the plurality of stacking portions, in accordance with a location where the conveyance abnormality occurred and a type of the conveyance abnormality.