In order to satisfactorily transmit audio data of various formats through a transmission line, when data having a predetermined data length as a unit is transmitted by a predetermined format between devices connected to a predetermined transmission line, label data indicating a system of transmitted audio data is located at a starting portion of the data having the predetermined data length, sub-label data is located at an interval behind label data if necessary and data accompanying with audio data is located and transmitted, whereby a side which receives this data can easily identify a system of audio data or the like.