The present invention provides a bolt that can exhibit a looseness-prevention function even though the bolt is repeatedly attached and detached. A bolt 1 includes a groove 4 that extends along a helix of a screw thread 3 and that is provided on a peak 31 of the screw thread 3. Further, the bolt is configured to include a plurality of the grooves 4 being spaced apart from each other along a helical direction of the screw thread 3.