In a navigation system in which the page data loaded from a server are displayed in a terminal, the server receiving the request for data loading from the terminal transmits the requested data if the data generation has ended, but, if not, estimates the end time and transmits the estimated end time together with display information indicating that the data generation is in progress. The terminal, issuing the request for data loading, displays the display data received in response to the request, and, if the estimated end time of data generation is received together with the display data, issues the request for data loading again when the estimated end time is reached. Thus efficient processing can be realized without wasted waiting time or wasted request for data loading in the terminal, in case the data generation requires a long time.