A communication system includes a communication device functioning as a master device and a plurality of slave devices communicably connected to the communication device via a communication line, the communication device setting a prescribed address in an added slave device based on a position of the added slave device in a topology composed of a plurality of slave devices, judging whether a change has possibly occurred in the topology when the prescribed address is set in the added slave device, if there is an erroneously set slave device whose address was erroneously set, specifying that slave device, when it is judged that a change has possibly occurred, and resetting the address of the specified erroneously set slave device to an original address.