A post-processing unit is disposed so as to face the apparatus side surface of a printer that has a manual feed tray protruding from the apparatus side surface. The post-processing unit has an ejection tray, which is movably provided in a unit body and to which paper accepted from the printer is ejected. In an apparatus height direction crossing a direction in which paper is ejected, the ejection tray can be moved to a first position at which ejected paper can be mounted and to a second position at which part of paper mounted on the manual feed tray can be supported.

A square back processing unit performs a square back process on the sheet bundle and includes a pair of clamp portions. The sheet bundle subjected to the square back process by the square back processing unit is discharged to a sheet bundle discharge unit. A cover unit is provided downstream of the square back processing unit in the conveyance direction such that a child access probe according to a safety standard IEC 62368-1 does not reach the pair of clamp portions in a case where the child access probe is inserted from an outside of the sheet processing apparatus.

A conveyance unit conveys the sheet to an accumulation portion. A half-folding processing unit includes a folding roller pair and performs a half-folding process on the sheet bundle. A conveyance roller pair conveys the sheet bundle. A square back processing unit performs a square back process on the sheet bundle and includes a pair of clamp portions. A length of a conveyance path from the folding roller pair to the pair of clamp portions is larger than a half of a length of a long side of a sheet of a maximum size. In a state in which conveyance by the conveyance roller pair of a first sheet bundle to be subjected to the square back process is stopped, the conveyance unit conveys at least one sheet included in a second sheet bundle subsequent to the first sheet bundle toward the accumulation portion.

A blanks storage unit for storing a stack of blanks includes: inlet and outlet sections of the blanks; a feed device having a support device to restingly receive the blanks of the stack of blanks; and a feed element for moving the blanks along a feed trajectory from the inlet section towards the outlet section. The unit also includes a guide device. At least one of the support device or the guide device is movable with respect to the other along a lifting trajectory between a transport configuration, in which said support device defines in the section a feed plane of the blanks and the blanks rest on the support device, and a sliding configuration in which the guide device is at least partially lifted with respect to the support device and the blanks rest on the guide device to be guided, sliding along the section towards the outlet.