Each of a plurality of dwelling buildings includes a dwelling parent device, a management office parent device, and a building control unit communicatively connected to each dwelling parent device in the host building and the management office parent device in the host building via an intercom line. The building control units are interconnected via a network that is connected with a management center that includes a centralized management office parent device and a centralized control unit connected to the centralized management office parent device via the intercom line. The building control unit in each dwelling building can set a calling time zone in which it is possible to call the centralized management office parent device or the management office parent device of other building, in addition to the management office parent device in the host building. When there is a calling from the dwelling parent device in the set calling time zone, the management office parent device in the host building receives a calling signal from the dwelling parent device and the building control unit also receives the calling signal from the dwelling parent device and transmits the calling signal to the centralized management office parent device or the management office parent device of the other building.