An identification number setting system includes a first element component including a first storing section, coupled to a first branch communication line branching from a main line of a bus-type communication wire, and coupled to a power supply, a second element component including a second storing section, coupled to a second branch communication line branching from the main line, and coupled to the power supply to be capable of switching energization and disenergization, and a control device coupled to the main line and configured to communicate with the first element component and the second element component. The control device writes a first identification number in the first storing section in a first state and writes a second identification number different from the first identification number in the second storing section after the writing of the first identification number and in a second state.