A striking portion 7 is formed with a fixed anvil 17 and a movable anvil 19 arranged to be able to advance into a striking path 18 to be opposed to the fixed anvil 17. A forming and striking mechanism 8 is constituted by a driver plate 9 for striking out a staple at the striking path 18 from the striking path 18, and a forming plate 10 for forming a plurality of unformed staple members arranged above the movable anvil 19 and the fixed anvil 17 in the striking path 18 simultaneously in a C-shape. The unformed staple members are formed in the C-shape by operating the forming plate 10 and thereafter, the driver plate 9 is operated on a plane the same as that of the forming plate 10.