A transmission device includes an optical amplifier to amplify an optical main signal to be transmitted on an optical transmission path; a first controller to stop output of the optical amplifier and output of an optical monitor signal to be transmitted on the optical transmission path when a failure of the optical transmission path is detected; a second controller to be switched from the first controller and to operate and stop the output of the optical amplifier and the output of the optical monitor signal when the failure of the optical transmission path is detected; an optical monitor signal transceiver to transmit and receive the optical monitor signal including control information; and a switch to switch an operation from the first controller to the second controller, based on information of the failure of the optical transmission path based on the states of transmission and reception of the optical monitor signal.