A network facsimile system is configured such that telephone numbers which a relay server can user are assigned to communication terminals. When a image is transmitted from the communication terminals to destinations outside the network facsimile system via the relaying server, the assigned telephone numbers are used as station signal numbers. When an image is transmitted to the relaying server from origins outside the network facsimile system, destination communication terminals are identified based on the telephone numbers assigned thereto and receiving telephone numbers. Then, the image received by the relaying server is transmitted to the identified communication terminals.