IFAX is installed in securities firm A. PC is installed in a customer B and the other IFAX is installed in a branch C. IFAX transmits and receives image data between PC and IFAX via LAN and the Internet by use of e-mail. While, IFAX is connected to PSTN. IFAX transmits and receives facsimile data between G3FAX and IFAX via PSTN. IFAX transmits and receives image data among PC and the other IFAX and G3FAX and transmits the same image data to a host computer installed in a center in reduction in communication costs with respect to the center.