To provide a post-process apparatus which can perform a post process without reducing productivity by speedily recognizing a positional shift and suppressing the deterioration of the quality of paper sheet arrangement, even when the position of an alignment member shifts because of user's contact or the like.

A post-process apparatus which includes a discharge tray for stacking discharged paper sheets and a paper sheet alignment member for aligning the paper sheets on the discharge tray includes a position detection means for detecting the position of the paper sheet alignment member, and a control means which determines that the paper sheet alignment member shifts from a prescribed working range on the basis of position detection information obtained by the position detection means.