Stapler unit in which a stapler main body is swingable about its binding portions

A stapler unit comprising:

• a stapler main body having binding portions in a front end portion thereof, for stapling an end portion of recording sheets stored in a tray in a state that the end portion of the recording sheets is set between the binding portions;
• stapler moving means for moving the stapler main body along a side of the recording sheets;
• binding angle changing means comprising:
• a pivot provided on or in the vicinity of an axis of the binding portions, for rotatably supporting the front end portion of the stapler main body;
• and
• a driving system for swinging the stapler main body about the pivot within a given angular range,
• wherein the binding angle changing means changes a binding angle formed by the side of the recording sheets and the stapler main body by using drive force of the driving system;
• and
• advance/retreat means for advancing and retreating the stapler main body perpendicularly to the side of the recording sheets between a retreat position that is distant from the side of the recording sheets and a binding position where the binding portions are to bite the end portion of the recording sheets.