BUCHRÜCKENBILDUNGSVORRICHTUNG, NACHBEARBEITUNGSVORRICHTUNG, BUCHRÜCKENBILDUNGSSYSTEM UND BUCHRÜCKENBILDUNGSVERFAHREN

An spine formation device (3; 3A) includes a sheet conveyer (31) that conveys the bundle of folded sheets (SB) in a sheet conveyance direction, first and second sandwiching units (32,325,326) disposed downstream from the sheet conveyer (31), a contact member (330) disposed downstream from the second sandwiching unit (325,326), against which the folded portion (SB1) of a bundle of folded sheets (SB) is pressed, and a controller (110). The controller (110) stops the sheet conveyer (31) after the bundle is transported a predetermined distance from a contact position between the contact member (330) and the folded portion (SB1) of the bundle, causing the bundle to bulge, and causes the first and second sandwiching units (325,326) to squeeze the bulging of the bundle (SB) sequentially with the folded portion (SB1) of the bundle pressed against the contact member (330) to form a spine of the bundle.