An IP packet priority control system of the present invention transmits and receives an IP packet among a terminal on the Internet, a server, and a router operating under program control, and includes means for setting priority in an IP packet on a session-by-session basis in order to realize an IP packet priority control system which distributes load to hardware, performs priority control on a session-by-session basis, and causes no interference between images and control information. The session comprises a voice call, image data, and a JAVA applet of a browser. The IP packet priority is set such that the priority of control information of the voice call is high, the priority of the image data of the browser is low, and the priority of the JAVA applet is intermediate. The means for setting priority in an IP packet performs setting on a session-by-session basis in which a terminal or a server adds priority parameter passing to a standard API rather than setting on a port-by-port basis in which a router prioritizes control information with QoS control.