When a serial digital transfer interface transmission packet in which an interval of each line of a video frame comprises an area into which an end synchronizing code EAV is inserted, an area into which header data is inserted, an area into which a start synchronizing code SAV is inserted and a payload area into which data containing video data and/or audio data is inserted is transmitted, a transmission packet is generated by inserting frame sequence data for managing the phase of the audio data into the payload area at its audio item portion of a header area corresponding to an audio data block area into which the audio data is inserted and transmitted in the form of serial data. Also, a transmission packet is generated by inserting not only the frame sequence data but also data indicative of the number of audio samples contained in a frame indicated by the frame sequence data into an audio sample count area corresponding to the audio data block area and transmitted.