The book binding device includes a section for forming a cut in the end side of a conveyed sheet, a control section for controlling the section for forming a cut, and a selection section for selecting each sheet for the presence/absence of a cut to be formed by the section for forming a cut, wherein the control section controls the formation of a cut by the section for forming a cut based on the presence/absence of the formation of a cut selected by the selection section, and then the mixture of sheets in which cuts are formed and sheets in which cuts are not formed are bundled and bound to complete a booklet.