Spine formation device, post-processing apparatus, spine formation system, and spine formation method

An spine formation device includes a sheet conveyer that conveys the bundle of folded sheets in a sheet conveyance direction with a folded portion of the bundle forming front end portion thereof, first and second sandwiching units disposed downstream from the sheet conveyer, a contact member disposed downstream from the second sandwiching unit, against which the folded portion of a bundle of folded sheets is pressed, and a controller. The controller stops the sheet conveyer after the bundle is transported a predetermined distance from a contact position between the contact member and the folded portion of the bundle, causing the bundle to bulge, and causes the first and second sandwiching units to squeeze the bulging of the bundle of folded sheets in a thickness direction sequentially with the folded portion of the bundle pressed against the contact member to form a spine of the bundle.