The present invention, when the rockfall prevention fence strain deformation in the optical fiber is caused, and to quickly detect the strain in fact the rockfall prevention fence, can be easily installed in a holding of rockfall prevention fence generic to prevent various types of rockfall fence not only can be used easily as ever, it is not damaged due to falling rocks occur, it will readily related to falling rocks detection device configured to recycling by the return circle.
According to the present invention, the hollow compression spring which emit the pressure in the 110 and the upper fixing member 12 which supports the one end of the outer case 11, a compression spring 13, which is formed, the compressed state to the bottom 13, and the hollow (110) sliding inside by bending the optical fiber 20 has a sliding member 14 of the outer case 11, the sliding member 14 from falling to the optical fiber when pressing the optical fibers 20 It is configured to support 20, including the stop pin (30) for fixing the position of the lower modified receiving member 15 and the sliding member 14 to allow the optical fiber 20 can be bent; The wire mesh 102 is deformed or holding 100 is when when taking over wire 103 ppophige from the sliding member 14, so the pull-modified sliding member 14 from falling by the force of the compression spring 13, the optical fiber ( 20) a modification by falling rocks detection device characterized in that it detects whether a modification of the rockfall prevention fence to result in the light refraction of the optical fiber (20).