A constructed system includes multiple clients, a server like a print portal, and multiple printers connecting with a network. A client transmits a printing requirement, which specifies a content of interest to be printed and a printer as an output resource, to the print portal. The print portal transmits the specified content of interest to the specified printer, which then carries out the actual printing operation. A security system interposed between the print portal and the printer in principle refuses transmission of data from the print portal, but allows transmission of the printing requirement from the client when direct communication between the printer and the client is established by means of infrared ray or feeble radio wave. This arrangement ensures the sufficient level of security, while enhancing utility of printing via the network.