A sheet processing apparatus which makes it possible to detect staples at a plurality of points by a smaller number of sensors. The sheet processing apparatus shifts a stapler along an edge of a sheet bundle. The stapler has a staple detection sensor attached thereto. The staple detection sensor detects a staple driven into the sheet bundle while passing by a staple detection position during shifting of the stapler. The stapler sequentially performs stapling at a first position and a second position along the edge of the sheet bundle, and is then shifted to a standby position. During a time period from completion of the stapling at the first position to completion of the shifting of the stapler to the standby position, the staple detection sensor detects presence or absence of a staple at each of the first position and the second position.