A rotation suppressing member 211 is fixed to a detection optical fiber 103a of a curved shape sensor. The rotation suppressing member 211 is located within the space defined by ring members 201, guides 204 and CH tube 208 with being in contact with the ring members 201, guides 204 and CH tube 208. In this manner, the rotation suppressing member 211 suppresses rotation of the detection optical fiber 103a.
