PURPOSE: To improve productivity in butt joint work by making both extremities of a staple intersect each other when stapling is completed, and plunging them into a mating member.

CONSTITUTION: A staple 27 is supplied to a driver guide groove 6 of a nose of a nailing machine from a staple magazine. On both sides of the driver guide groove 6, rising walls 7a and 7b are provided. The staple 27 is pressured at its crown 29 by a plate-like driver and it arrives at a staple extremity guide groove 24 formed into a tapered shape by sliding on the inner wall faces of the rising walls 7a and 7b. Extremities 28 of the staple 27 extend vertically from the crown 29, and inclined faces 28d extending from tips 28b at the inner faces of the extremities 28 to the middle of the outer faces are formed. Accordingly, when the crown 29 of the staple 27 is completely driven until it abuts against the surface of a material to be stapled, the extremities 28 intersect and intrude from one member to other member.