To provide a sheet processing device that binds a bundle of sheets in a shorter time.

The sheet processing device includes: a conveyance belt 5; concavo-convex disk-shaped rotators 1A, 1B having concave and convex formed in outer circumferences and forming concave and convex portions on a sheet S during rotation by nipping the sheet S to be conveyed by the conveyance belt 5; and concavo-convex disk-shaped rotators 2A, 2B. Regarding the bundle of sheets where a lowermost sheet, an interposed sheet and an uppermost sheet are stacked in the order, when the interposed sheet is arranged to protrude from the lowermost and uppermost sheets, the concavo-convex disk-shaped rotators 1A, 1B rotate by nipping protruding parts the lowermost and uppermost sheets, and the concavo-convex disk-shaped rotators 2A, 2B rotate by nipping protruding parts of the lowermost and uppermost sheets, to configures a sheet binding device 200 for forming the concave and convex portions.