A system for inspecting an optical transmission path constituted of a plurality of optical fibers, comprising: a first inspecting device (10A; 10C) configured to be provided on one end side of the optical transmission path; a second inspecting device (10B; 10C) configured to be provided on another end side of the optical transmission path; and a loss calculating unit configured to calculate a loss of each of the plurality of optical fibers, wherein each of the first and second inspecting devices has a light source unit (11; 61) outputting test light (TL; TLa; TLb; TLc), a plurality of light input/output ports each detachably connected to each of the plurality of optical fibers, an optical switch selectively coupling the light source unit with each of the light input/output ports, a first light detecting unit detecting a first intensity of the test light input from the inspecting device on a counterpart side and passing through the optical switch, a second light detecting unit detecting a second intensity of the test light directed from the light source unit toward the optical switch, a third light detecting unit optically coupled to another end of a test optical fiber having one end connected to each of the plurality of light input/output ports in place of each of the plurality of optical fibers, and detecting a third intensity of the test light received from the light source unit via the test optical fiber, and an internal loss recording unit recording a loss of an optical path inside the device obtained on a basis of a difference between the third intensity and the second intensity, and wherein the loss calculating unit calculates a loss of each of the plurality of optical fibers on a basis of a value obtained by subtracting the first intensity of the second inspecting device, a loss recorded in the internal loss recording unit of the first inspecting device, and a loss recorded in the internal loss recording unit of the second inspecting device from the second intensity of the first inspecting device. a first inspecting device (10A; 10C) configured to be provided on one end side of the optical transmission path; a second inspecting device (10B; 10C) configured to be provided on another end side of the optical transmission path; and a loss calculating unit configured to calculate a loss of each of the plurality of optical fibers, wherein each of the first and second inspecting devices has a light source unit (11; 61) outputting test light (TL; TLa; TLb; TLc), a plurality of light input/output ports each detachably connected to each of the plurality of optical fibers, an optical switch selectively coupling the light source unit with each of the light input/output ports, a first light detecting unit detecting a first intensity of the test light input from the inspecting device on a counterpart side and passing through the optical switch, a second light detecting unit detecting a second intensity of the test light directed from the light source unit toward the optical switch, a third light detecting unit optically coupled to another end of a test optical fiber having one end connected to each of the plurality of light input/output ports in place of each of the plurality of optical fibers, and detecting a third intensity of the test light received from the light source unit via the test optical fiber, and an internal loss recording unit recording a loss of an optical path inside the device obtained on a basis of a difference between the third intensity and the second intensity, and a light source unit (11; 61) outputting test light (TL; TLa; TLb; TLc), a plurality of light input/output ports each detachably connected to each of the plurality of optical fibers, an optical switch selectively coupling the light source unit with each of the light input/output ports, a first light detecting unit detecting a first intensity of the test light input from the inspecting device on a counterpart side and passing through the optical switch, a second light detecting unit detecting a second intensity of the test light directed from the light source unit toward the optical switch, a third light detecting unit optically coupled to another end of a test optical fiber having one end connected to each of the plurality of light input/output ports in place of each of the plurality of optical fibers, and detecting a third intensity of the test light received from the light source unit via the test optical fiber, and an internal loss recording unit recording a loss of an optical path inside the device obtained on a basis of a difference between the third intensity and the second intensity, and wherein the loss calculating unit calculates a loss of each of the plurality of optical fibers on a basis of a value obtained by subtracting the first intensity of the second inspecting device, a loss recorded in the internal loss recording unit of the first inspecting device, and a loss recorded in the internal loss recording unit of the second inspecting device from the second intensity of the first inspecting device.