To prevent deterioration in communication quality by reducing a data quantity to be inserted (stored) in a payload so as to reduce a delay time.

The device is provided with a cell assembly means 1 that inserts transmission data to a payload of an asynchronous transfer mode(ATM) cell so as to assemble the data into cells and transmits the cell to an ATM network 2 and with a cell disassembly means 3 that receives the ATM cell sent via the ATM network 2 and disassembles the cell to decode original data. A cell processing section 11 of the cell assembly means 1 of the transmitter side divides the payload of the ATM cell into 1st and 2nd areas, transmission data are inserted only to the 1st area and the 2nd area is set idle to send the ATM cell to the ATM network 2. On the other hand, a receiver side cell disassembly means 3 extracts data from the 1st area when the original data are decoded.