PURPOSE: To facilitate disposition and installation and to substantially prevent damaging by curving plural times or spirally winding the optical fiber sensor in a sheet-shaped support.

CONSTITUTION: The optical fiber sensor 1 is curved many times in the sheet- shaped support 2 and the radiations, liquid or gas, etc., leaking from the surface region of the wall surface of a structure, etc., is detected. The wiring and installation of the optical fiber sensor to the structure, etc., are facilitated in this way and the optical fiber sensor which is hardly damaged is obtd. The same result is attained even if the optical fiber sensor is spirally wound.