A measurement system for inspecting an optical transmission line (R) including a plurality of optical fiber lines (fr), the system comprising: a measurement device including a light source configured to output testing light, and a first power meter configured to measure intensity of light; and one or a plurality of connection members each configured to optically connect a pair of optical fiber lines of the plurality of optical fiber lines (fr), wherein a first optical fiber line of the pair of optical fiber lines includes a first end (2a 1 ) and a second end (2b 1 ) opposite to the first end (2a 1 ), a second optical fiber line of the pair of optical fiber lines includes a third end (2a 2 ) and a fourth end (2b 2 ) opposite to the third end (2b 1 ), the one or plurality of connection members optically connect the second end (2b 1 ) to the fourth end (2b 2 ), the light source is configured to cause the testing light to be incident on the first end (2a 1 ), the first power meter is configured to measure a first intensity which is the intensity of the first output light output from the third end (2a 2 ) by causing the testing light to propagate through the pair of optical fiber lines, characterized in that each of the one or plurality of connection members includes a coupler having two inputs and two outputs, the two outputs of the coupler are optically connected to each other, the second end (2b 1 ) and the fourth end (2b 2 ) are optically connected to the two inputs of the coupler , wherein the measurement device further includes a second power meter configured to measure a second intensity which is the intensity of the second output light output from the first end (2a 1 ), and the second output light is obtained by demultiplexing the testing light by the coupler. a measurement device including a light source configured to output testing light, and a first power meter configured to measure intensity of light; and one or a plurality of connection members each configured to optically connect a pair of optical fiber lines of the plurality of optical fiber lines (fr), wherein a first optical fiber line of the pair of optical fiber lines includes a first end (2a 1 ) and a second end (2b 1 ) opposite to the first end (2a 1 ), a second optical fiber line of the pair of optical fiber lines includes a third end (2a 2 ) and a fourth end (2b 2 ) opposite to the third end (2b 1 ), the one or plurality of connection members optically connect the second end (2b 1 ) to the fourth end (2b 2 ), the light source is configured to cause the testing light to be incident on the first end (2a 1 ), the first power meter is configured to measure a first intensity which is the intensity of the first output light output from the third end (2a 2 ) by causing the testing light to propagate through the pair of optical fiber lines, characterized in that each of the one or plurality of connection members includes a coupler having two inputs and two outputs, the two outputs of the coupler are optically connected to each other, the second end (2b 1 ) and the fourth end (2b 2 ) are optically connected to the two inputs of the coupler , wherein the measurement device further includes a second power meter configured to measure a second intensity which is the intensity of the second output light output from the first end (2a 1 ), and the second output light is obtained by demultiplexing the testing light by the coupler. <EOS>