OPTICAL TRANSMISSION SYSTEM

PROBLEM TO BE SOLVED: To provide an optical transmission system where communication control with high quality is conducted between a terminal station device and a relay device so as to efficiently and precisely retrieve fault location. SOLUTION: An optical monitor signal generating means 11 monitors the operating state of own device and input and output signals, on the basis of a monitor control instruction to generate an optical monitor signal. A light pulse signal transmission means 12 transmits a light pulse and an inverted light pulse to an optical transmission line, on the basis of a fault retrieval control instruction. A monitor control instruction transmission means 21a transmits a monitor control instruction. A monitor processing means 22a recognizes an operating state and identifies a faulty block, on the basis of the optical monitor signal. A fault retrieval control instruction transmission means 21b transmits a fault retrieval control instruction. A Rayleigh scattered light read means 22b conducts read processing of Rayleigh scattered light, by using the inverted light pulse for a synchronizing signal. A fault detection means 23b detects fault on the optical transmission line, on the basis of a result of reading of the Rayleigh scattered light.