A special playback request made by a user is input into a special playback controller. Transmission data to be transmitted to a decoding terminal based on the special playback request and insertion data to be transmitted together with the transmission data are read from a data storage unit. Used bits of the read transmission data and insertion data which occupy a vbv buffer are detected by a vbv delay detector. A stuffing insertion unit adds extra data to the read insertion data based on the detected used bits so as to adjust the data size of the insertion data. The resulting transmission data and the insertion data are selectively output by a switch based on the type of special playback operation indicated in the special playback request. The output transmission data and the insertion data are then transmitted to the decoding terminal.