PURPOSE: To enable simple, flexible and cost effective laying of optical fibers by forming the plural ductlets formed in a pipeline into a structure capable of loosely housing the optical fibers, housing the optical fiber into the one ductlet and forming the other ductlets to be in an empty state as a structure for newly inserting optical fibers in the future.

CONSTITUTION: The pipeline 11 is internally provided with the plural ductlets 12 respectively forming tubular progressing paths. The plural ductlets 12 are formed to the structure capable of loosely housing the lightweight and flexible optical fibers. The lightweight and flexible optical fiber 14 are housed in at least one of the ductlets 12. At least the other ductlets 12 are formed to the empty state as the structure to be freshly inserted with the optical fibers in future. Then, the optical fiber cable having the ductlets of the empty state is previously laid and thereafter, the addition of the fresh optical fibers by utilizing the flow of a gaseous medium when needed is made possible. As a result, the post addition of the optical fibers and the maintenance are facilitated and the initial cost and maintenance cost are drastically reduced.