9. The apparatus of claim 8 , wherein the error detector comprises: an n-gram generation unit configured to generate the forward and backward morpheme sequences by binding morphemes arranged in a forward direction and a backward direction, respectively, from the respective morphemes broken up from the input sentence in the preset window size; a search unit configured to search whether the forward morpheme sequences and the backward morpheme sequences generated by the n-gram generation unit are in the example-based index DB; a suitability calculation unit configured to extract the frequencies of appearance at which the forward morpheme sequences and the backward morpheme sequences generated by the n-gram generation unit are identical to morpheme sequences retrieved by the search unit, and calculate suitability scores based on the extracted frequencies of appearance; and an error determination unit configured to detect grammatical errors by determining whether the suitability scores calculated by the suitability calculation unit are smaller than a threshold or whether the suitability scores are smaller than the threshold by a predetermined value or more.
9. The apparatus of claim 8 , wherein the error detector comprises: an n-gram generation unit configured to generate the forward and backward morpheme sequences by binding morphemes arranged in a forward direction and a backward direction, respectively, from the respective morphemes broken up from the input sentence in the preset window size; a search unit configured to search whether the forward morpheme sequences and the backward morpheme sequences generated by the n-gram generation unit are in the example-based index DB; a suitability calculation unit configured to extract the frequencies of appearance at which the forward morpheme sequences and the backward morpheme sequences generated by the n-gram generation unit are identical to morpheme sequences retrieved by the search unit, and calculate suitability scores based on the extracted frequencies of appearance; and an error determination unit configured to detect grammatical errors by determining whether the suitability scores calculated by the suitability calculation unit are smaller than a threshold or whether the suitability scores are smaller than the threshold by a predetermined value or more. 11. The apparatus of claim 9 , wherein the suitability calculation unit is configured to calculate the suitability scores by applying different weights according to frequencies of appearance at which respective morphemes are identically arranged in the morpheme sequences retrieved by the search unit.