There is provided a relay device capable of simultaneously transmitting various additional information such as audio information, character information, and image information while suppressing the communication cost and the line use ratio without increasing the calculation cost in the decoding process. The relay device includes an encoded information analysis unit (602) which outputs transmission mode information and an additional information flag to an additional processing unit (603) and outputs an information source code of each layer to the additional processing unit (603) according to the transmission mode information. According to the combination of the transmission mode information and the additional mode information, the additional processing unit (603) performs additional processing of the additional information for the information source code of each layer. An encoded information integration unit (604) integrates the transmission mode information, the additional mode information, the additional information flag, and various information source codes inputted from the additional processing unit (603).