Abstract
A sheet postprocessing apparatus includes a postprocessing device that performs postprocessing on a sheet, and a drive unit having a motor for transporting the sheet. The postprocessing device includes an optional unit mounting base. On the optional unit mounting base, one of a folding unit having a function to fold the sheet, and a basic unit without the folding function can be selectively mounted. When the folding unit is mounted on the optional unit mounting base, a bidirectional motor capable of rotating forward and reversely is additionally provided in the drive unit, in addition to a forward rotation motor capable of rotating forward, which is permanently provided.