If a new AV device is connected to an IEEE 1394 network, and if the subunit type of the newly connected AV device is an unregistered subunit type, then a microprocessor of a gateway downloads a CGI and a Web page generation module, both corresponding to the newly connected AV device, to the gateway from an information device on an IP network or from the newly connected AV device. Thus, using the Web page generation module corresponding to the newly connected AV device, the microprocessor of the gateway can automatically generate a Web page to operate such new AV device. Hence, using the Web page sent from the gateway and using the CGI (command conversion module), which is stored in the gateway and which corresponds to the newly connected AV device, an information device on the IP network can control the newly connected AV device, wherein the latter information device for control of the newly connected AV device can be either the same as or different from the former information device for download of the CGI and the Web page generation module.