A transmission device includes a frame processing unit, a redundant channel processing unit, a transmission and reception unit, and a channel selection unit. The frame processing unit generates division frames, adds error detection signals to the division frames, and outputs the division frames to which the error detection signals are added to a plurality of data channels. The redundant channel processing unit generates, from the division frames, one or more redundant frames including restoration information that enables restoration of the division frames, and outputs the generated redundant frames to a data channel. The transmission and reception unit outputs the division frames and the redundant frames to a transmission line. The channel selection unit allocates the division frames and the redundant frames to allocable transmission and reception units.