Post-processing apparatus

A post-processing apparatus configured to perform a predetermined process after an image forming process performed by an image forming apparatus and eject a sheet stack after the predetermined process, the post-processing apparatus comprising:

• a tray onto which the sheet stack is ejected;
• an ejector which sends the sheet stack in an ejection direction to eject the sheet stack;
• a pushing mechanism including a pushing portion configured to push the sheet stack against the tray;
• a motion detector configured to detect a motion of the pushing mechanism;
• and
• a controller including an ejection controller configured to control the ejector,
• wherein the pushing mechanism moves the pushing portion in a first direction away from the tray when the ejector ejects the sheet stack to the tray under control by the ejection controller,
• wherein the pushing mechanism moves the pushing portion in a second direction which is opposite to the first direction when the ejector finishes ejection of the sheet stack to the tray under control of the ejection controller, and
• wherein the ejection controller executes interruption control of interrupting the ejection of the sheet stack unless the motion detector detects the motion of the pushing mechanism moving the pushing portion in the first direction when the ejector ejects the sheet stack to the tray under control of the ejection controller.