Digital audio data which have a predetermined packet structure are divided into units including a predetermined number of bits; each unit of the divided digital audio data is converted into specific data to be encoded; the encoded data are arranged in blanking intervals of video data; the digital audio data are transmitted as well as the video data using a transmission line for the video data, and the video data and the audio data may be simultaneously and favorably transmitted, adopting an existing video-data transmission format such as the DVI standard.