The fiber sensor is laid on a detection object which can be bent at least in part and is arranged along the longitudinal direction of the detection object in a detection target range (DR) which is at least a part of the detection target, and one or A state of a detection target range of an object to be detected can be detected by detecting light that is guided through at least one optical fiber, comprising at least one optical fiber (30) having a plurality of parts to be detected . Assuming that the inflection point of the shape of the detection target range assumed from the shape that can be taken by the detection target range of the detection target or the state that can be detected in the detection target range is the assumed inflection point (581, 582), at least one The optical fiber has the number of assumed inflection points plus one or more detected parts (321, 322, 323).ファイバセンサは、少なくとも一部が湾曲可能な検出対象物に敷設され、検出対象物の少なくとも一部である検出対象範囲(DR)に前記検出対象物の長手方向に沿って配置され、1つ又は複数の被検出部を有する、少なくとも一本の光ファイバ(30)からなり、少なくとも一本の光ファイバ内を導光した光を検出することで、検出対象物の検出対象範囲の状態を検出できる。検出対象物の検出対象範囲が取り得る形状又は検出対象範囲において検出可能な状態から想定する、検出対象範囲の形状の変曲点を想定変曲点(581,582)とすると、少なくとも1本の光ファイバは、想定変曲点の数+1個以上の被検出部(321,322,323)を有する。
