1. An extensible-markup-language Path Language (XPath) evaluating method for evaluating the XPath relevant to an extensible-markup-language (XML) document by use of a computer, the XPath evaluating method comprising: a first step of serially inputting XML event strings constituting an XML document to be processed; a second step of serially evaluating the XPath respectively relevant to the inputted XML events and retaining information concerning a result of partial evaluation of the XPath in given storing means when the XPath is partially established woth respect to a given XML event; and a third step of repeating the partial evaluation of the XPath along with the input of the XML event strings while considering the result of the partial evaluation retained in the storing means and evaluating that the XPath is established with respect to the XML document when the last part of the XPath is established.