Abstract: A threaded fastener and a connector having the threaded fastener are provided, which threaded fastener includes: a shank, with a screw thread thereon, to be screwed to a mating member; and a head continuing from the shank and having a regular-polygonal cross section, wherein the head has an expanding portion with a cross-sectional area gradually becoming larger toward the shank and a reducing portion with a cross-sectional area gradually becoming smaller toward the shank, the reducing portion continues from the expanding portion in a direction of an axis of the shank, and the reducing portion is arranged nearer the shank than the expanding portion.