1. A method for establishing paraphrasing data for a machine translation system comprising: selecting a paraphrasing target sentence through application of an object language model to a translated sentence that is obtained by machine-translating a source language sentence; extracting, from a corpus DB for the source language, paraphrasing candidates that can be paraphrased with the selected paraphrasing target sentence; performing machine translation with respect to the extracted paraphrasing candidates; selecting a final paraphrasing candidate from the extracted paraphrasing candidates by applying the object language model to a result of the machine translation with respect to the extracted paraphrasing candidates; and confirming a paraphrasing relationship of the paraphrasing target sentence and the selected final paraphrasing candidate as paraphrasing lexical patterns using a bilingual corpus and storing the paraphrasing lexical patterns in a paraphrasing DB.