To enable to screw in as simply and quickly as possible only by inserting and turning without applying a force.

This fastener combines a shaft 1 with screw threads formed on the outside surface and a nut 2 with screw grooves formed on the inside surface of the opening part. In this case, the shaft 1 has a screw thread that forms a non-thread surface 13 along the shaft direction. In the opening part of the nut 2, an inside surface 24 without screw groove is formed at the position corresponding to the part forming screw thread part 14 on the shaft 1. A thread groove part 23 to be screwed in the screw thread part 14 is formed at the position corresponding to the part forming the non-thread surface 13 of the shaft 1.