The intercommunication system according to the invention is an intercommunication system used in an apartment complex comprising plural residential buildings. Each of the plural residential buildings is equipped with room parent devices installed in respective rooms; a collective entrance device which enables a call manipulation for calling one of the room parent devices; and a building control unit which connects, by an intercom line, the collective entrance device and the room parent devices of the respective rooms of the residential building. The collective entrance device has a storage unit which is stored with terminal information of the collective entrance device. The building control units of the plural respective residential buildings are connected to each other by a network in which a communication is performed according to a general-purpose protocol and can communicate, over the network, with an external apparatus that is connected to an external network.