A surgical stapling instrument having a staple fastening assembly including a curved cartridge device. The device has at least one curved open row of staples having a first and second ends and having a concave side and a convex side. Opposite to the cartridge device there is a curved anvil for forming the ends of the staples. The instrument also includes a moving device adapted to move the anvil with respect to the cartridge device in a parallel relationship. The instrument also includes a staple driving device adapted to drive the staples out of the cartridge device towards the anvil, and a knife. The knife has opposing first and second sides and is contained in the cartridge device. There is also a knife actuating device adapted to move the knife towards the anvil. The instrument includes staple fastening assembly having a retaining pin which moves between the cartridge device to align them. The retaining pin is located on the second side of the knife in an intermediate region between the first end and second ends of the curved row of staples.