A sheet processing apparatus includes a conveying portion; a conveying path for sheets conveyed by the conveying portion; a stack portion where sheets discharged from the conveying path are stacked; a first binding portion moving in a crossing direction crossing the conveying direction; a first regulating portion regulating a position of a sheet bundle stacked on the stack portion; a first guide member guiding the first regulating portion; a second regulating portion regulating a position of a sheet bundle on the stack portion in the crossing direction; a second guide member guiding the second regulating portion; a third regulating portion regulating a position of a sheet bundle on the stack portion in the conveying direction; and a second binding portion binding a corner portion of a sheet bundle without a staple. The first binding portion binds a corner portion of a sheet bundle by a staple.