PROBLEM TO BE SOLVED: To provide a new screw fastening structure having a loosening prevention function.SOLUTION: A screw fastening structure includes a first screw element 11, and a second screw element 12 screwed to the first screw element 11. Any of the first and second screw elements has an engaging recess R opened toward the other side, and the other has an engaging protrusion P inserted into the engaging recess R in a fastening state. An inner circumferential surface of the engaging recess R is configured in the shape of a straight cylinder along an axial direction. The engaging protrusion P is configured in a pillar shape or a cylindrical shape having a maximum diameter part at one place in the axial direction. The maximum diameter part of the engaging protrusion P and the inner circumferential surface of the engaging recess R is made relatively eccentric so as to be brought into pressure contact only in a portion of the circumferential direction in the fastening state. The maximum diameter part of the engaging protrusion P is provided by having a predetermined distance from the proximal end of the engaging protrusion P so as to axially reciprocate to the engaging recess R while being brought into pressure contact only in a portion of the circumferential direction to the inner circumferential surface of the engaging recess R.SELECTED DRAWING: Figure 1COPYRIGHT: (C)2020,JPO&INPIT【課題】 緩み止め機能を有する新規なねじ締結構造を提供する。【解決手段】 第１ねじエレメント１１と、第１ねじエレメント１１に対してねじ締結される第２ねじエレメント１２とを備え、第１及び第２ねじエレメントのいずれか一方は、他方側に向けて開口する係合凹部Ｒを有し、他方は、締結状態で係合凹部Ｒに挿入される係合凸部Ｐを有する。係合凹部Ｒの内周面は、軸方向に沿って真っ直ぐな円筒状に構成される。係合凸部Ｐは、軸方向１箇所に最大径部位を有する円柱状若しくは円筒状に構成される。係合凸部Ｐの最大径部位並びに係合凹部Ｒの内周面が、締結状態で周方向一部のみにおいて圧接されるように、相対的に偏心している。係合凸部Ｐの最大径部位は、係合凹部Ｒの内周面に対して周方向一部のみにおいて圧接した状態で係合凹部Ｒに対して軸方向に進退可能なように、係合凸部Ｐの基端部から所定の距離を有して設けられる。【選択図】 図１
