A stapler 100 is provided with a driver 5 provided at a forward end of the driver arm 4, as shown in FIG. 20A , driving a staple 30 out according to any predetermined clinching force, the driver 5 having projections 5b, 5b which contact portions of the staple 30 over the legs of the staple pushed against the front inner wall of the magazine 3 by a staple-pushing member 40. Accordingly, the clinching force is transferred to the legs through the projections 5b, 5b of the driver 5 so that the clinching force can be concentrated onto the legs. Furthermore, a staple-pushing member 40 pushes the staple 30, so that it is possible to prevent buckling from occurring in the legs.