A transmitting apparatus is used in an electrical frequency division multiplex transmission system including nodes that are on an optical transmission path and that respectively frequency-multiplex a sub-carrier of a unique frequency and a carrier wave to transmit information to a receiving apparatus on the optical transmission path. The transmitting apparatus is disposed in each node and includes a determining unit that receives an input of information concerning unused sub-carriers of a transmission signal in the optical transmission path and determines transmission of the information to the receiving apparatus using an unused sub-carrier; an electrical frequency division multiplex transmission unit that using a frequency of the unused sub-carrier determined by the determining unit, modulates the input information to be transmitted to the receiving apparatus; and a coupling unit that adds to the transmission signal in the optical transmission path, a modulated modulation signal.