Sheet post-processing apparatus that carries out stapling process on sheet bundle and control method therefor

A sheet post-processing apparatus that carries out a stapling process on a plurality of sheets, comprising:

• a sheet stacking unit configured to have the plurality of sheets stacked thereon as a sheet bundle;
• a sheet stapling unit configured to stapling the sheet bundle, stacked on said sheet stacking unit, using a binding needle at a stapling process position at which the stapling process is carried out;
• a folding process unit configured to, after the stapling process, carry out a folding process in which the sheet bundle is folded at a position of the binding needle;
• a binding needle detection unit configured to be disposed at a predetermined location between the stapling process position and a folding process position at which the folding process is carried out, and detect the binding needle;
• a sheet bundle moving unit configured to move the sheet bundle from the stapling process position to the folding process position;
• and
• a correction unit configured to, based on a moving distance of the sheet bundle before the binding needle is detected by said binding needle detection unit after the stapling process by said sheet stapling unit, corrects a position of a subsequent sheet bundle with respect to said sheet stapling unit in the stapling process for the subsequent sheet bundle.