To improve positioning of middle folding and saddle stitching and simplify the apparatus in structure.

This apparatus is provided with a paper setting table 3 having a slit 7 for setting a plurality of sheets of stacked paper P1, a middle folding stitching plate 16 which is movably mounted between a waiting position not entering the slit 7 of the paper setting table 3 and a middle folding and stitching position entering the slit 7 and comprises a staple bending part 19 at an entering tip of the slit 7, and a stapler 20 for stapling the paper P1 through which the middle folding stitching plate 16 is in pressure contact with the stapler 20 in a position of middle folding and stitching. In cooperation with operation of a handle 12 the middle folding and stitching plate 16 moves between the waiting position and the middle folding and stitching position.