To provide a bolt which can be fastened without using a special tool and cannot be loosened after it is fastened, but which can be loosened in an emergency.

This bolt includes a first bolt including a hollow part at a center and provided with first serration at one end, a second bolt having a lower half body slidably inserted in the hollow part and provided with second serration at one end, and a lock part provided at another end of the second bolt, and includes a first locking part to be a locking part during rotation in one direction but not to be a locking part during rotation in a reverse direction on a head part of the first serration, and a second locking part locking on the first locking part provided on the first serration and rotating the first serration only in one direction on a surface facing the first serration of the second serration.