A network data processing system is provided suitable for achieving reduction of network traffic volume and shortening of the time elapsed before first print out. A client unit generates printing data formed by segmenting data with respect to each component that constitutes printing contents, transmits a printing request including header information to a printer, searches for partial data from inside a storage part in response to an acquisition request, and transmits the retrieved partial data to the printer. When the printing request is received, the printer analyzes the received printing request, determines whether or not the partial data required for forming the printing data is stored in a storage part, acquires insufficient partial data from the client unit having a small hop count, stores the acquired partial data in the storage part, and forms the printing data based on the partial data of the storage part.