To provide a staple using insertion-cutting blades that are manufacturable inexpensively, by which the strength of the insertion-cutting blades that are necessary when penetrating binding sheets is secured and the penetration of a staple through the binding sheets is executed reliably. The stapler is constituted by including a handle, a frame and a base. The frame is provided, in the vicinity of the front edge portion of a feeding path through which the interlinked staples are fed, with a driver executing the penetration of the staple with respect to the binding sheets. Punching blades are mounted respectively on the right and the left of a staple push down unit at the lower edge portion of the driver main body portion. Each punching blade has a predetermined length and is provided with a blade edge at one edge portion. Also, each punching blade is provided, in the vicinity of the edge portion including the blade edge, with a protrusion portion which has a slope surface at least on a side of the blade edge and which is protruded by a predetermined amount thereof. Here, the protrusion portion is not formed with the full width of the cutting blade, and each cutting blade has a linear portion that is continuous from one edge portion to the other edge portion in the longitudinal direction.