A paper post-processing device includes: a base tray 112 configured to stack paper transferred from an image-forming device; a paper transferring unit including a paper gripper configured to grip a rear end of a paper bundle stacked on the base tray 112, a paper transferring unit configured to transfer the paper gripper; and a stacker tray 103 configured to stack paper transferred from the paper transferring unit, wherein the paper gripper includes an ejector 202 to be fixed, and a gripper 106 rotatably configured about a predetermined angle to the ejector 202, and the paper gripper is configured to grip the several sheets of paper by the ejector 202 and the gripper 106, further including a grip release unit configured to release a grip by the ejector 202 and the gripper 106.