To avoid the lowering of conveying accuracy and the occurrence of conveying displacement due to the excessive number of overlapping sheets by minimizing the number of overlapping sheets when sheets are overlappingly conveyed in a post-processing apparatus.

This post-processing apparatus includes a post-processing part which performs post-processing for a sheet discharged from a former-stage apparatus, a post-processing time calculating part which calculates a time required for the post-processing based on the content of the post-processing, a time comparing part which compares the time required for the post-processing and a sheet interval between the sheets discharged from the former-stage apparatus, an overlappingly conveying part which overlappingly conveys a plurality of sheets discharged from the former-stage apparatus on the upstream side of the post-processing part, and a control part which controls the overlappingly conveying part. The control part changes the number of overlapping sheets in the overlappingly conveying part according to a sheet interval between the sheets discharged from the former-stage apparatus where the time required for the post-processing is determined to exceed the sheet interval based on the comparison result of the time comparing part.