A paper-made staple binds a sheet bundle subjected to folding processing by a folding blade and a folding roller. The paper-made staple includes a pair of leg portions inserted into the sheet bundle and then bent inward; and a connection portion that connects the leg portions in a staple longitudinal direction. The connection portion has, at an edge portion thereof, a cut in a direction crossing the longitudinal direction so as to correspond to a predetermined folding position of the sheet bundle for the purpose of facilitating the folding of the connection portion, and the cut is formed inward from the edge portion so as to have a substantially triangular shape and is provided on both edge portions of the connection portion of the paper-made staple.