A structured document including a first element which includes an attribute that handles values as character strings, and a second element which defines a change of the values of the attribute is acquired. The attribute is extracted from the first element, and the extracted attribute is converted into a child element of the first element. The second element is converted into a third element which defines a change of the values of the attribute converted into the child element. The structured document updated by the conversions is output as a structured document.