When image communication is conducted by using one of a plurality of different image communication systems via a sending/receiving path including an IP network (101), a transmitter (105) and receivers (108, 108a, 112, 115) or devices (gateway (111, 113) or an IP network interface (109)) for relaying the image communication existing in the sending/receiving path store SDP media stream descriptions, which include different image communication systems usable by the transmitter and receivers, in an SIP message and send the SIP message, and select an image communication system for use in practical image communication in given order of priority and image communication control parameters to be used in the appropriate image communication system, on the basis of the SDP media stream descriptions. Whereby, an appropriate image communication system can be automatically selected from various image communication system that can be used between a calling terminal and a called terminal, without a need for a complicated operating procedure or setup procedure.