A disclosed optical add/drop multiplexing device demultiplexes a first signal into multiple signals according to wavelengths, drops one or more of the demultiplexed signals to a transponder, adds one or more signals output from the transponder, multiplexes these signals into a second signal, and outputs it. The device includes an injecting unit for injecting one of measurement signals, each of whose wavelength corresponds to that of a different demultiplexed signal, into a core of a multicore cable within the device, the core being used to transmit the different demultiplexed signal having the corresponding wavelength; a preventing unit for preventing the one measurement signal from emanating; a measuring unit for measuring, for each wavelength, levels of the one measurement signal before and after the corresponding core; a calculating unit for calculating loss of the corresponding core, based on the measured levels; and an informing unit for reporting the calculated loss.