A sheet processing apparatus and an image forming apparatus can secure the stackability of a sheet when discharging a residual sheet. When a residual sheet is conveyed from a main body of an image forming apparatus to a first sheet stacking portion at turning on the power for the main body of the image forming apparatus, the trailing edge of the residual sheet is aligned first by a trailing edge aligning portion. And then, a residual sheet is moved to a sheet discharging position, in which the sheet is discharged onto a second sheet stacking portion, while the residual sheet, the trailing edge of which has been aligned, is being held by a holding member.