An inserting section (1) of a manipulator includes a moving section (12) on the end. The moving section (12) operates with displacement of wires (13) driven by a driving section (21). Potentiometer sections (33) are provided with the wires (13). Reflecting surfaces (42) the reflectance of which continuously varies in the longitudinal direction are fixed in parts penetrating the potentiometer sections of the wires (13). Light emitted from a light source (351) is guided by optical fibers (31) one end of which is fixed to the potentiometer section (33), and is irradiated onto the reflective surfaces (42). The intensity of the light reflected by the reflective surfaces (42) varies with displacement of the wires (13). The reflected light is guided by the optical fibers (31) to an optical section (35), and is received by light receiving element (352), resulting in the displacement of the wires (13) being calculated by signal processing section (36).
