PURPOSE: To provide a nail unbending even at the time of being driven by a hammer so as to be able to obtain strong holding force without the nail head becoming trumpet-shaped.

CONSTITUTION: Screw blades 1a, 1b, 1c of triangular cross section are provided around a shank part 1, and a disc shape head part 2 is provided at one end of the shank part 1. A semi-spherical protruding part 2a is provided at the center of the head part 2 where the centerline of the shank part 1 passes, and a conical tip part 3 pointed at the angle of 25° is formed at the tip of the shank part 1. The screw blades 1a, 1b, 1c are made gradually higher toward the head part 2 side from the tip part 3 side.