Sheet processing apparatus featuring relatively-displaced stapled sheet bundles and related method

A sheet processing apparatus, comprising:

• sheet conveying means for conveying sheets;
• first loading means for loading a sheet bundle comprising a plurality of sheets conveyed by the sheet conveying means;
• first and second lateral aligning means for aligning the opposite side edges of the sheet bundle loaded on the first loading means in the direction perpendicular to the sheet conveying direction by moving between retreat positions out of contact with the sheet bundle and lateral aligning positions in contact with the sheet bundle;
• stapling means for performing a stapling treatment with respect to a sheet bundle aligned by the first and second lateral aligning means;
• sheet bundle conveying means for conveying a sheet bundle stapled by the stapling means;
• second loading means for loading sheet bundles conveyed by the sheet bundle conveying means;
• and
• loading position control means for controlling a time at which the first and second lateral aligning means move from their aligning positions to their retreat positions for each sheet bundle,
• wherein, during loading of sheet bundles onto the second loading means, the first and second lateral aligning means move together to displace along the sheet conveying direction the loading positions of successive sheet bundles.