To permit the address of an indoor machine easily to be set.

In the indoor machine address setting method for an air- conditioning system 10, whose first refrigerant system 11 and second refrigerant system 12 are constituted of outdoor machines 13 and indoor machines 14 which are connected through a refrigerant pipeline and whose communication circuit 15 is constituted of the plurality of outdoor machines and indoor machines in the refrigerant system which are connected by a first communication wire 15A, a second communication wire 15B and a third communication wire 15C, the outdoor machine of respective refrigerant systems cuts communication with the outdoor machines of other refrigerant systems through the third communication line and carries out the communication employing the indoor machines in the same refrigerant system, the first communication line 15A and the second communication line 15B respectively whereby the address is set in the indoor machines in the same refrigerant system.