A measurement system (10, 10A) for inspecting an optical transmission line including a plurality of optical fiber lines (fr), the system (10, 10A) comprising: a measurement device (20, 20A) 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 (50, 50A) 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 (50, 50A) 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 (20, 20A) 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 (20, 20A) 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 (50, 50A) 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 (50, 50A) 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 (20, 20A) 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.