A light-transmission-path-spectrum measurement device, compri sing: wavelength varying OTDR measurement means for varying and generating a wavelength of measurement light to be transmitted to a first light transmission path, and also measuring return light acquired from the measurement light being returned, by a plurality of repeaters connected to the first light transmission path, via a second light transmission path connected to the repeaters; optical signal multiplexing means for selecting the wavelength of the measurement light being generated by the wavelength varying OTDR measurement means, and outputting the selected wavelength to the first light transmission path; control means for controlling the wavelength of the measurement light being generated by the wavelength varying OTDR measurement means and the wavelength of the measurement light being selected by the optical signal multiplexing means; and measurement data processing means for processing measurement data about the return light being measured by the wavelength varying OTDR measurement means, wherein the control means controls the wavelength varying OTDR measurement means in such a way as to perform sweeping across a wavelength band of the first light transmission path while switching the wavelength of the measurement light to be generated, wherein the wavelength varying OTDR measurement means acquires a cable trace across a wavelength band of the first light transmission path, wherein the measurement data processing means extracts peak level of cable trace in each wavelength of the measurement light for each position of the first light transmission path and acquires the peak level in each position of the first light transmission path over different wavelengths. wavelength varying OTDR measurement means for varying and generating a wavelength of measurement light to be transmitted to a first light transmission path, and also measuring return light acquired from the measurement light being returned, by a plurality of repeaters connected to the first light transmission path, via a second light transmission path connected to the repeaters; optical signal multiplexing means for selecting the wavelength of the measurement light being generated by the wavelength varying OTDR measurement means, and outputting the selected wavelength to the first light transmission path; control means for controlling the wavelength of the measurement light being generated by the wavelength varying OTDR measurement means and the wavelength of the measurement light being selected by the optical signal multiplexing means; and measurement data processing means for processing measurement data about the return light being measured by the wavelength varying OTDR measurement means, wherein the control means controls the wavelength varying OTDR measurement means in such a way as to perform sweeping across a wavelength band of the first light transmission path while switching the wavelength of the measurement light to be generated, wherein the wavelength varying OTDR measurement means acquires a cable trace across a wavelength band of the first light transmission path, wherein the measurement data processing means extracts peak level of cable trace in each wavelength of the measurement light for each position of the first light transmission path and acquires the peak level in each position of the first light transmission path over different wavelengths.