<p>An electronic device system (10) includes an electronic device unit (parent device) (1) connected to an external device (5) and a plurality of electronic device units (child devices) (2 to 4) connected in series to it. An initialization instruction from a CPU (20) of the parent device (1) turns off all the switches (22) for opening/closing the RS-485 line connecting all the electronic device units. The parent device (1) successively generates identification codes (ID). A parent device (1) starts to set the code as its ID and turns on the switch (22) of the electronic device unit after the setting is complete. Thus, ID's are automatically set from the parent device (1) to the child devices (2 to 4) successively in the order of the connection.</p>
