1. A data processing method for a portable communication terminal connected to a server over a communication network, comprising: predicting a future change in a communication state of a connection between the portable communication terminal and the server based on a record of communication speed recorded in reference to the connection; determining a terminal processing level indicating a level of data which is permitted to be held in the portable communication terminal based on the future change in the communication state that has been predicted; determining an importance level for each type of data of one or more types of data; and limiting data to be held in the portable communication terminal based on the terminal processing level that has been determined and on the importance level that has been determined for each type of data.