To provide a fastening bolt applicable to a narrow place where a wrench is hardly put in, and repeatedly usable.

The fastening bolt 1 is intended for planting the same in a base, for instance, mounting a machine and fastening the machine with a nut 2. In contrast to a screw 12 on the tip side of the bolt body 10, a screw 11 on the base side is set at a left-handed screw. With this, the fastening bolt becomes applicable to a narrow place where a wrench is hardly put in. Further, since the bolt body 10 is not forcedly screwed in a nut different in the size of its pitch, the screw thread is not collapsed, and repeated use is possible.