Abstract: This invention relates to an ATM cell multiplexing/demultiplexing apparatus for inserts simple routing information in corresponding bits within an ATM cell and performing cell multiplexing/demultiplexing operation between a single ATM layer device and a number of physical layer devices using the routing information, the apparatus comprises: a decoding/demultiplexing unit for extracting routing information from a header of each ATM cell transmitted from the ATM layer device and demultiplexing the ATM cell according to the routing information extracted into the number of physical layer devices; an ATM cell multiplexing unit for multiplexing the ATM cells transmitted from the number of physical layer devices into the ATM layer device; a receiving routing unit for inserting routing information within a header of each ATM cell multiplexed by the ATM cell multiplexing unit; and a micro bus interface unit for interfacing the ATM layer device and the number of physical layer devices with respect to system operation a