An optical wavelength multiplex transmission system comprising a redundant configuration composed of an active system and a standby system including first and second optical lines that are connected between each of a plurality of first terminal station apparatuses and a second terminal station apparatus, wherein each of the first terminal station apparatuses comprises: first and second couplers (32a, 32b) provided for the first and second optical lines, respectively; a light source configured to generate dummy light; a selective switch configured to select one of the first and second couplers (32a, 32b) corresponding to the standby system and supply the dummy light to the selected coupler; and a control unit configured to control the selective switch and vary intensity of the dummy light, the control units of the first terminal station apparatuses being configured to vary the intensity of the dummy light with different varying patterns for the plurality of the first terminal station apparatuses, the second terminal station apparatus comprises: third and fourth couplers (33a, 33b) provided for the first and second optical lines, respectively, and configured to extract the dummy light; and first and second detectors (34a, 34b) connected to the third and fourth couplers (33a, 33b), respectively, and configured to detect a varying pattern of intensity of the extracted dummy light, and the optical wavelength multiplex transmission system is configured, according to the varying pattern of the dummy light detected by one of the first and second detectors (34a, 34b) corresponding to the standby system, to identify a route of the standby system between one of the first terminal station apparatuses and the second terminal station apparatus, and determine whether there is no failure in the standby system, each of the first terminal station apparatuses comprises: first and second couplers (32a, 32b) provided for the first and second optical lines, respectively; a light source configured to generate dummy light; a selective switch configured to select one of the first and second couplers (32a, 32b) corresponding to the standby system and supply the dummy light to the selected coupler; and a control unit configured to control the selective switch and vary intensity of the dummy light, the control units of the first terminal station apparatuses being configured to vary the intensity of the dummy light with different varying patterns for the plurality of the first terminal station apparatuses, first and second couplers (32a, 32b) provided for the first and second optical lines, respectively; a light source configured to generate dummy light; a selective switch configured to select one of the first and second couplers (32a, 32b) corresponding to the standby system and supply the dummy light to the selected coupler; and a control unit configured to control the selective switch and vary intensity of the dummy light, the control units of the first terminal station apparatuses being configured to vary the intensity of the dummy light with different varying patterns for the plurality of the first terminal station apparatuses, the second terminal station apparatus comprises: third and fourth couplers (33a, 33b) provided for the first and second optical lines, respectively, and configured to extract the dummy light; and first and second detectors (34a, 34b) connected to the third and fourth couplers (33a, 33b), respectively, and configured to detect a varying pattern of intensity of the extracted dummy light, and third and fourth couplers (33a, 33b) provided for the first and second optical lines, respectively, and configured to extract the dummy light; and first and second detectors (34a, 34b) connected to the third and fourth couplers (33a, 33b), respectively, and configured to detect a varying pattern of intensity of the extracted dummy light, and the optical wavelength multiplex transmission system is configured, according to the varying pattern of the dummy light detected by one of the first and second detectors (34a, 34b) corresponding to the standby system, to identify a route of the standby system between one of the first terminal station apparatuses and the second terminal station apparatus, and determine whether there is no failure in the standby system,