The Internet printing system for a client perform printing out to a print server that cannot circumvent a firewall by the Internet Printing Protocol (IPP). For a print server which cannot circumvent the firewall by IPP, a proxy unit which can communicate using IPP is installed on the Internet. A server site of the print server is opened on the proxy unit, and an IPP client regards the print server as a public IPP server opened on the Internet, and exchanges printing service requests and responses via the proxy unit. Since the proxy unit performs gateway conversion from IPP into another protocol, the client can print out to the print server circumventing the firewall by using IPP.