To provide an address setting method and device by which an address of a terminal is automatically set in a short time.

First an island unit 10 transmits an address setting reset signal to a communication line 30 to bring each of board units 21-23 not to output a signal to an output terminal. Then the island unit 10 transmits an address setting request signal including an address to the communication line 30 in a state that the signal is outputted to the output terminal of the island unit 10. The board unit 21 whose input terminal receives a signal and whose output terminal has no signal output sets the address included in the address setting signal as its own address. Then a setting response signal is sent to the communication line 30 and the signal is outputted to an output terminal. Upon the receipt of the setting response signal, the island unit 10 sends an address setting request signal including a next address to the communication line 30. Similarly to the above, addresses are sequentially set to the board units 22, 23.