A communication system, having a base unit, which is communicably connected to an external communication device, and at least one extension unit, which is communicable with the base unit and with the other extension unit and the external communication device via the base unit, is provided. The base unit includes an information collecting system to collect information of the at least one extension unit in the communication system. The at least one extension unit includes an information obtaining system to obtain the information from the base unit and an indicating system to indicate presence and communication status of each of the at least one extension unit in the communication system based on the obtained information individually on an extension unit basis.