In a multiplexing method of multiplexing communication signals from communication signal transmitting sections and transmitting a multiplexed signal to a multiplexed signal receiving section, each of the communication signals, an identification address preassigned to a predetermined signal identifying section through which a communication signal passes in a multiplexing system including the communication signal transmitting section and the multiplexed signal receiving section is added to each communication signal. The resultant signal is output. The identification address is extracted from each output signal. The respective communication signals are multiplexed on the basis of the extracted identification addresses. A multiplex apparatus, access network system, protocol termination apparatus, and multiplexing/demultiplexing apparatus are also disclosed.