To provide a sheet processing apparatus which can reliably align a plurality of stacked sheets even if there are conveyance error and differences in length in a conveyance direction, and to provide an image forming apparatus.

The lowermost sheet S1 is sequentially transferred out of sheets S1, S2 conveyed to an intermediate processing tray 138 by a draw-in belt roller so that the sheets S1, S2 contact with a rear end stopper 150. Moreover, a paddle 131 is located in an upstream transfer direction of the draw-in belt roller 158 to transfer the sheets S1, S2 conveyed to the intermediate processing tray 138 and convey them to the draw-in belt roller, wherein the paddle is driven so that the next sheet S2 does not reach the draw-in belt roller 158 until the sheet S1 transferred by the draw-in belt roller 158 contacts with the rear end stopper 150.