When XML data stored in a server are to be updated, a client displays an update form by using update form display means. The update form includes paths, methods and values (after addition or change) of elements of XML data. Then, the paths, methods and values are inputted into input boxes in the update form. Then, an update instruction is generated on the basis of the information inputted into the input boxes, and is transferred to data update mean in the server. Thus, the client need not to convert the XML data into the DOM object, and a memory capacity of the client is reduced, because the update instruction includes only the paths, methods and values.