A sheet processing apparatus includes a conveying portion, a stack portion on which sheets are stacked, a first binding portion moving in a crossing direction crossing a conveying direction, a first regulating portion regulating a position of a sheet bundle stacked on the stack portion in the crossing direction, a first rack moving in the crossing direction with the first regulating portion, a first pinion forming a rack-pinion mechanism with the first rack, a second regulating portion regulating a position of a sheet bundle stacked on the stack portion in the crossing direction, a second rack moving in the crossing direction with the second regulating portion, a second pinion forming another rack-pinion mechanism with the second rack, a third regulating portion regulating a position of a sheet bundle stacked on the stack portion, and a second binding portion which binds a corner portion of a sheet bundle without a staple.