The present invention provide a transmission system comprising a transmission apparatus for transmitting audio data of multi channels and auxiliary data required for playback of the audio data, and a receiving apparatus for receiving the audio data and the auxiliary data which are transmitted by the transmission apparatus. A multiplexer of the transmission apparatus creates block data that is composed of 8 frames, and first 1 byte of each frame is allocated to a header having Sync, OE and the like, the second byte is allocated to the auxiliary data including AUX data and copyright protect information, and remaining bytes are used to transmit the audio data. An encryptor carries out an encryption process for the second and later bytes of each frame, and a communication means outputs encrypted data. A communication means of the receiving apparatus receives the encrypted data from the transmission apparatus, a decoder decodes the encrypted data, and a demultiplexer demultiplexes the audio data and the auxiliary data. Therefore, this transmission system transmits multi-channel audio data of the DVD-Audio or the like efficiently on a transmission line using fixed length frames according to the MOST method, and takes measures for copyright protection of audio data.