The present invention provides a method and system to improve the accuracy of natural language processing systems by enabling them to acquire a parsing output that is accurate to a degree for any type of sentence. The feature of the present invention is that a sentence (a non-grammatical, ill-formed sentence) that cannot be parsed when using a conventional parsing process, which relies on grammatical knowledge, is re-analyzed by using the parsing results for an identical word row in a sentence (a well-formed sentence) in the same context that could be parsed. More specifically, the processing below is performed: (1) a well-formed sentence in a context that includes a word row that is identical to a word row in an ill-formed sentence is searched for, and a dependency structure for that word row is extracted from the parsing results for the well-formed sentence; and (2) the dependency structures of the phrases obtained in (1) are linked by referring to linking information for the well-formed sentence and a grammar, and the dependency structure of the entire sentence is introduced.