A client computer can display a desired Web screen on a display by transmitting a request containing an URL address to a Web server using a Web browser. The Web server provides an instance associated with a URL address with member variable mode indicating whether a variable can be rewritten in response to a request from the Web browser. Only when member variable mode indicates that the variable can be rewritten, the Web server rewrites the variable corresponding to a request from the Web browser. On the other hand, when member variable mode indicates that the variable cannot be rewritten, the Web server does not rewrite the variable and notifies the Web browser of an error. This control can prevent the occurrence of inconsistency between the data recognized as the data which the user has input to the Web browser and transmitted to the Web server and the data actually stored in the Web server.