7. The apparatus of claim 6 , wherein the error post-processing unit comprises: a post-processing target detector detecting whether the sentence boundary candidate is a post-processing target or not, based on the predetermined rule; and an error corrector changing the classification result of the sentence boundary candidate into the opposite when the sentence boundary candidate is detected as a post-processing target.
6. The apparatus of claim 1 , further comprising an error post-processing unit correcting an error based on a predetermined rule with respect to the classified sentence boundary candidate, wherein the sentence generating unit extracts the sentence units from the document based on the classification result corrected by the error post-processing unit.