To provide a packet transmitter-receiver unnecessitating the buffers of nearly the same capacity to each of a receiving system and a transmitting system.

An external synchronization control means 26 ertracts identification information from a packet 6 to write in a buffer for synchronization 25. When identification information 12 which should be transmitted to the buffer 25, the means 26 realize the processing of generating the packet 6 including only identification information 12. As the buffer 25 must store only identification information extracted from the packet 6, the capacity of the buffer 25 is smaller than that of a transmission and reception buffer 24 housing the packet 6. Consequently there is no need to prepare a buffer of a capacity for storing the packet 6 for housing identification information 12 to refer to. Namely it is not necessary to provide two groups of buffers of nearly equal quantity.