To make automatically executable the generation and allocation of addresses by storing a unit identification part in a storage element in response to a selected input, establishing another unit identification part for a detector and preparing a circuit for holding a separation element at a low impedance state.

A system 10 automatically allocates respective indicators or addresses for plural members 20 based on the slight interference of a control element 12. The process is started by a unit 12-1 through the control element 12. When there is a branch line 14a for one communication, the process is propagated from a starting unit to the right in each unit in a direction separated from a power supply. When a communication link includes branch lines 14a, 14b, the starting unit executes determination related to a propagation direction. When each system includes a link branching like a branch line 16, the same address as units on the branch line 14a corresponding to the starting unit is allocated to the starting unit.