In order to improve the reliability of a reconfigurable optical add/drop multiplexing (ROADM) device, provided is an optical add/drop device that comprises the following: a first wavelength selection unit and a second wavelength selection unit that can select and output an optical signal of a prescribed wavelength from among inputted optical signals; a first branching unit that selectively outputs a first signal being an optical signal that has been inputted from a first terminal station on a main route to the first wavelength selection unit and the second wavelength selection unit; a second branching unit that selectively outputs a second signal being an optical signal that has been inputted from a second terminal station on a sub-route to the first wavelength selection unit and the second wavelength selection unit; and a first output unit that can selectively output to the second terminal station, as a third signal, either the optical signal outputted by the first wavelength selection unit on the basis of the first signal and the second signal, or the optical signal outputted by the second wavelength selection unit on the basis of the first signal and the second signal.