A language conversion system converts an original sentence in a source-language into a translated sentence in a target-language. The language conversion system includes a original analysis unit for analyzing the original sentence so as to obtain an intermediate structure of the original, an idea center extraction unit for extracting an idea center from the intermediate structure obtained by the original analysis unit, the idea center being a central expression of an idea to be described by a sentence, an identification unit for identifying a sentence pattern including the idea center extracted by the idea center extraction unit, an information extraction unit for extracting information required by the sentence pattern identified by the identification unit from the intermediate structure of the original sentence, a decision unit for deciding an intermediate structure of a translated sentence based on the sentence pattern and request information extracted by the information extraction unit, and a creation unit for creating a translated sentence in a surface level from the intermediate structure decided by the decision unit.