The present invention provides a transmission apparatus including transmitting side line interfaces which convert packet format data sent from an asynchronous network to a SONET/SDH frame format and then transmit the data, multiple receiving side line interfaces which receive the SONET/SDH frame format data and convert the data to packet format data and a circuit switching section which performs circuit switching. The transmitting side line interfaces include a variable length frame mapping section which converts the packet format data to variable length frame format data and a time division multiplexing mapping section which converts the variable length frame format data to the SONET/SDH frame format data. The receiving side line interfaces include a variable length frame demapping section which reconverts the SONET/SDH frame format data to variable length frame format data.