A post-processing apparatus for transferring sheets from a sheet carry-in port to a first post-processing section and a second post-processing section to execute post-processing such as stapling and sheet folding on the sheets, includes a sheet carry-in path located in a substantially horizontal direction. The sheets fed to the carry-in port are sequentially transferred to a predetermined sheet discharging port. A first switchback conveying path branches off from the sheet carry-in path so as to reverse a sheet conveying direction. The first post-processing section connected to the first switchback conveying path executes the post-processing on the sheets. A second switchback conveying path branching off from between the carry-in port and sheet discharging port of the sheet carry-in path is upstream of the first switchback conveying path so as to reverse the sheet conveying direction. The second post-processing section is located downstream of the second switchback conveying path.