A damage detection system comprising: optical paths that propagate lights in at least three different directions, the optical paths having at least two optical paths per one direction, wherein the optical paths are disposed so that any of combinations each consisting of not less than three optical paths, having directions different from each other, out of the optical paths do not intersect with each other at one position; a light source that makes the lights incident on one ends of the optical paths respectively; a photodetector that detects the lights output from other ends of the optical paths; and a signal processing system that specifies at least one location of damage based on optical detection signals detected by the photodetector, wherein the signal processing system is adapted to specify an area as the at least one location of the damage when each intensity of at least three lights output from at least one of the combinations each consisting of the not less than three optical paths having directions different from each other and propagating the at least three lights in the at least three different directions has decreased, the area including each portion of the at least one of the combinations each consisting of the not less than three optical paths having directions different from each other; and wherein the signal processing system is adapted to specify locations of damage corresponding to a plurality of the combinations each consisting of the not less than three optical paths having directions different from each other when each intensity of at least three lights output from each of the plurality of the combinations each consisting of the not less than three optical paths having directions different from each other has decreased. optical paths that propagate lights in at least three different directions, the optical paths having at least two optical paths per one direction, wherein the optical paths are disposed so that any of combinations each consisting of not less than three optical paths, having directions different from each other, out of the optical paths do not intersect with each other at one position; a light source that makes the lights incident on one ends of the optical paths respectively; a photodetector that detects the lights output from other ends of the optical paths; and a signal processing system that specifies at least one location of damage based on optical detection signals detected by the photodetector, wherein the signal processing system is adapted to specify an area as the at least one location of the damage when each intensity of at least three lights output from at least one of the combinations each consisting of the not less than three optical paths having directions different from each other and propagating the at least three lights in the at least three different directions has decreased, the area including each portion of the at least one of the combinations each consisting of the not less than three optical paths having directions different from each other; and wherein the signal processing system is adapted to specify locations of damage corresponding to a plurality of the combinations each consisting of the not less than three optical paths having directions different from each other when each intensity of at least three lights output from each of the plurality of the combinations each consisting of the not less than three optical paths having directions different from each other has decreased.