The present invention relates to a sheet processing apparatus comprising an intermediate staking portion for aligning a sheet sent, a reference wall for positioning the sheet, a stapler form performing a binding operation with respect to a sheet bundle aligned by the reference wall, delivery means for delivering the sheet bundle from the intermediate stacking portion, a sheet stacking portion for stacking the sheet bundle and guide means provided above the sheet stacking portion and at an end portion on the stapler side of the end portions in the width direction of the sheet. The guide means supports an end portion on the stapler side of the sheet bundle when the sheet bundle is delivered from the delivery means in a staple mode in which the binding operation is preformed with respect to the sheet bundled.