A sheet processing apparatus (PD) for an image forming apparatus (PR) is configured so as to be capable of preventing the misalignment of the end edge of sheets to be scooped and transported from an intermediate tray, and reliably preventing the so-called displacement of end edges in the post-processing steps of sheets as a recording medium with an image formed thereon, and thereby preventing the inferior appearance during binding. A sheet folding apparatus (G) enables a user to easily adjust the misalignment of the fold line of sheets that occurs during actual use, in the middle folding processing steps of sheets as a recording medium with an image formed thereon.