Post-processing device and image forming apparatus

An image forming apparatus comprising:

• an image forming section configured to form an image on a paper;
• and
• a post-processing devices configured to subject a stack of paper sheets to be stapled to stapling, the stack of paper sheets comprising a plurality of paper having images formed thereon by the image forming apparatus, wherein
• the post-processing device comprises:
• a tray capable of being loaded with the stack of paper sheets;
• a sheet output section configured to discharge the stapled stack of paper sheets from the tray;
• a stapler provided movably in a direction perpendicular to a direction of the discharge of the stack of paper sheets and configured to apply staples to a plurality of locations on the stack of paper sheets loaded on the tray;
• a sheet stack shifting section configured to shift the stack of paper sheets loaded on the tray in the direction perpendicular to the direction of the discharge of the stack;
• and
• an operation control section configured to control operations of the stapler and the sheet stack shifting section, and
• wherein the operation control section allows the stapler to apply a staple to a first one of the locations on the stack of paper sheets and then allows the stapler to move to a position corresponding to a second one of the locations to be stapled next on the stack of paper sheets while allowing the sheet stack shifting section to shift the stack of paper sheets in a direction opposite to a direction of the movement of the stapler.