Patent ID: 7660556

Claim:
A sheet post processing apparatus to produce a booklet, comprising: a folding device to carry out a booklet folding process by folding, at a time, either one sheet or a group of a plurality of sheets discharged from an image forming apparatus; a sheet stacking section to successively stack sheets for which the booklet folding process has been carried out; a binding device for binding the sheets stacked on the sheet stacking section; and a control device to control the sheet post processing apparatus; wherein the folding device further comprises: two folding plates which are capable of having a distance adjusted between the two folding plates and which come in contact with a surface of the either one sheet or a group of a plurality of sheets, the surface becoming an inner surface after the either one sheet or a group of a plurality of sheets have been folded; and wherein the control device controls the folding device so that the booklet folding process of the sheet is carried out at positions of two folding lines at a same time, the two folding lines being approximately parallel, thereby obtaining a square-shaped back of booklet.