A sheet post-processing apparatus, e.g., that is included in an image forming system, includes: a sheet stacking unit configured to stack a plurality of sheets of one or more printable media; a sheet alignment unit configured to align the plurality of sheets stacked in the sheet stacking unit; a pressing mechanism configured to press and hold the plurality of sheets stacked in the sheet stacking unit; and a stapling unit configured to staple the plurality of sheets aligned by the sheet alignment unit, the stapling unit being displaceable to a given position that avoids interference with the pressing mechanism while the sheet alignment unit performs a sheet alignment with respect to the plurality of sheets in the sheet stacking unit.