PURPOSE: To constitute the system optionally by allowing the system to cope easily with any combination of types and number of slave stations without need of revision of a control table in a master station and without need of assumption of types and number of slave stations to be used in advance.

CONSTITUTION: A master station (CCU) 101 receives data representing types and functions of slave stations from each of slave stations (LCU) 102-109 at the system start or the like and generates and stores a control data for each slave station based on the data and the master station (CCU) 101 uses the control table for data transmission. When the multiplex communication system is applied to an automobile or the like, the optimum system is built up by combining slave stations without revision of software and data of the master station. Furthermore, when the function of a vehicle is added or revised, it is coped with by addition of a slave station and change in the function setting only.