A method, apparatus, and system for evaluation of a faulty point in a multi-stage optical amplifying and repeating transmission line which provides a totally new technique for searching for faults neither of the typical “command response type” or the “DCR method”. When a fault occurs in an optical submarine cable, the profile exhibited by the optical spectral characteristics of the optical noise signal (ASE) successively amplified through the chain of optical amplifying repeaters at the downstream side of the faulty point changes in accordance with the number of the repeaters. The technique finds the number of the repeaters until the faulty point based on the change in the profile so as to evaluate the location of the faulty point and has a step (S11) of monitoring the optical spectrum at the light receiving end and a step (S12) of determining the location of the faulty point from the monitored optical spectrum.