This invention presents an apparatus for composing an ATM wrapper transmission block capable of handling plural pieces of program information transmitted in SDTI or IP packet commonly by a low overhead. Since the ATM wrapper transmission block conforms to both AAL1 system and AAL5 system, sequential connection is possible by changing over the AAL1 transmission and AAL5 transmission in the ATM wrapper layer. Further, by the AAL5 system, live transmission output of minimum transmission delay, and contribution output free from error can be issued at the same time, and therefore the error is corrected by referring to the reception data in the former, and the error is corrected by re-sending the error position data in the latter.