OPTICAL BRANCHING AND INSERTING DEVICE

PROBLEM TO BE SOLVED: To search for failure positions, even in a section incapable of searching the failure position hereto fore by providing plural optical circulators and providing these optical circulators with plural paths respectively. SOLUTION: An optical circulator 111 is further provided with a path 111-3, which outputs signal light that is inputted from a transmission line 2 to a transmission line 1 in addition to paths 111-1 and 111-2. An optical circulator 115 is further provided with a path 115-3 which outputs a signal light that is inputted from a transmission line 4 to a transmission line 3, in addition to paths 115-1 and 115-2. Furthermore, it is possible to search for a failure position in all the transmission lines 1 to 4, including sections where a failure position could be searched in the conventional system by using an optical branching and inserting device that has the three-way optical circulators 111 and 115 in this way and further performing measurement by using C-OTDR from a terminal station side.