A fiber sensor includes a light source, and an optical fiber having flexibility to guide light emitted from the light source. The optical fiber has at least one light characteristics conversion portion. The fiber sensor also includes a light-receiving unit to receive the light guided by the optical fiber, and an identification unit having a unique shape on an outer peripheral surface of the optical fiber as compared with a round shape. The identification unit is formed to have a shape enabling at least one of an installation position and posture of the light characteristics conversion portion provided on the optical fiber to be identified.