Spine formation device, saddle-stitch bookbinding apparatus, sheet-edge cutting apparatus, sheet processing apparatus, and image forming apparatus

A spine formation device includes a sheet conveyer, a presser, and a spine formation member. The sheet conveyer conveys a bundle of folded sheets with a folded portion of the bundle of sheets forming a front end portion of the bundle of sheets. The presser is disposed downstream from the sheet conveyer in a sheet conveyance direction in which the sheet conveyer conveys the bundle of sheets. The presser is movable to press opposed sides of the front end portion of the bundle of sheets. The spine formation member is movably disposed downstream from the presser in the sheet conveyance direction. The spine formation member includes a groove portion that contacts and positions the bundle of sheets to define an amount by which the bundle of sheets protrudes from the presser and a spine formation face that forms a spine at the folded portion of the bundle of sheets.