In an intercom system to be used in an apartment complex configured by residential buildings and a centralized building that can communicate with the residential buildings, the residential buildings includes: residential room master devices disposed in residential rooms collective entrance devices—which can communicate with the residential room master devices; and a building controller. The building controller has: a building controller ID that, when one of the residential room master devices is called from the centralized building via the building controller, is used in recognition in which the centralized building recognizes the building controller; and a collective entrance device ID that, when the one residential room master device is called from the centralized building via the building controller, is used in recognition in which the one residential room master device recognizes the building controller as a virtual collective entrance device that is different from the collective entrance devices.