Bookbinding unit that in binding an inner-leave sheet bundle together with a cover enables accurate binding of the cover onto the bundle's spine and meanwhile forms folding scores in the cover flaps. Furnished with: a stacking tray unit; a process path for sequentially transporting bundles from the tray unit into adhesive-application and cover-binding locations; an adhesive application unit, disposed in the adhesive-application location, that applies adhesive to bundles from the tray unit; a cover-supply unit that supplies covers to the cover-binding location; and a cover-binding unit, disposed in the cover-binding location, that binds sheet bundles from the adhesive-application location together with covers. The cover-binding unit has a shoulder-pressing unit that forms spine creases in the spine portion of the covers, and a flap-pressing unit that forms folds in the spine-creased sides of the covers.