PURPOSE: To simply and automatically generate or extinguish a nonreflective terminal unit at an optional position by forming irregular corrugated members having a prescribed radius out of a shape memory alloy.

CONSTITUTION: Two shape memory alloy plates 51, 52 are linearly connected by an electrically and thermally insulating member 53, and both ends of them are fixed to fixing members 56. DC power sources and switches 55 are connected to the plates 51, 52 respectively, and an optical fiber cord 14 to be measured is stuck to the plate 51. The plates 51, 52 memorize the irregularities of the prescribed radii of curvature, and they are returned to irregular shapes of a prescribed radii of curvature via the temperature rise when DC voltage is applied then and they are self-heated. When one plate 52 is excited, the other plate 51 is straightly stretched, no bend is applied to the optical fiber cord 14, and an nonreflective terminal unit is extinguished. When the plate 51 is excited and the optical fiber cord 14 is bent, the nonreflective terminal is generated. The plate 52 is stretched by the tensile force of the plate 51, and it is deformed into a straight plate.