There is provided a binding member. The binding member includes: an upper toothed part having projections and recesses for forming irregularities in a bundle of recording materials; and a lower toothed part having projections and recesses for forming irregularities in the bundle of recording materials and forming a pair with the upper toothed part. In at least one of the upper toothed part and the lower toothed part, in side surfaces of the recesses of one toothed part, when the upper toothed part and the lower toothed part are engaged, surfaces wide in a direction parallel to the pressing direction of the toothed parts are formed so as to be provided gaps between the upper toothed part and the lower toothed part.