An intercommunication system which is used in an apartment complex comprising plural residential buildings, each of the plural residential buildings comprising: room parent devices installed in respective rooms; a terminal device (10, 20) configured to enable a call manipulation for calling one of the room parent devices; and a building control unit configured to connect, by an intercom line, the terminal device and the room parent devices of the respective rooms of the residential building, wherein: the terminal device comprises a storage unit which is stored with terminal information of the terminal 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 are configured to communicate, over the network, with an external apparatus that is connected to an external network; the building control unit of each of the plural residential buildings comprises a building controller; and plural terminal devices being installed in at least one of the residential buildings; the building controller of the at least one residential building has a building storage unit which is stored with building terminal information that is a combination of pieces of terminal information stored in the storage units of the plural respective terminal devices in the at least one residential building. room parent devices installed in respective rooms; a terminal device (10, 20) configured to enable a call manipulation for calling one of the room parent devices; and a building control unit configured to connect, by an intercom line, the terminal device and the room parent devices of the respective rooms of the residential building, wherein: the terminal device comprises a storage unit which is stored with terminal information of the terminal 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 are configured to communicate, over the network, with an external apparatus that is connected to an external network; the building control unit of each of the plural residential buildings comprises a building controller; and plural terminal devices being installed in at least one of the residential buildings; the building controller of the at least one residential building has a building storage unit which is stored with building terminal information that is a combination of pieces of terminal information stored in the storage units of the plural respective terminal devices in the at least one residential building. the terminal device comprises a storage unit which is stored with terminal information of the terminal 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 are configured to communicate, over the network, with an external apparatus that is connected to an external network; the building control unit of each of the plural residential buildings comprises a building controller; and plural terminal devices being installed in at least one of the residential buildings; the building controller of the at least one residential building has a building storage unit which is stored with building terminal information that is a combination of pieces of terminal information stored in the storage units of the plural respective terminal devices in the at least one residential building.