To provide a compact post-processing apparatus that does not increase a footprint for the apparatus and can remove a sheet stacked in a former job even while the sheet is being stacked on a stacker.

The post-processing apparatus includes at least two stackers 4, 5 to have vertical two stages, the stackers stacking and storing sheets that are sequentially fed out from the image forming apparatus after post-processing. The stackers includes a sheet stacking unit for stacking the sheet on an upper stacker 5 out of the two stackers 4, 5, a sheet dropping unit for causing a lower stacker 4 to drop the sheets P stacked on the upper stacker 5 to feed the sheet; and a sheet removing unit for removing the sheets dropped on the lower stacker 4 outside the post-processing apparatus. The lower stacker 4, when withdrawn, can be done even while the following job is being stacked on the upper stacker 5.