To easily and surely perform screwing-in work of a headed screw having an annular head part of an annular ring shape.

A screw part 12 projects to the radial directional outside from a circumferential directional part of an annular head part 11 of an annular ring shape. A shaft-like projection 13 projects to the radial directional inside from the circumferential directional part of the annular head part 11. The shaft-like projection 13 is held by a screwing-in tool to prevent the annular head part 11 from rotating in the circumferential direction R at screwing-in time.