1. A system for estimating a language model weight, the system comprising: a first search unit which receives a speech feature vector converted from a speech signal, performs a first search by applying a first language model to the received speech feature vector, and outputs a word lattice and a first acoustic score of the word lattice as a continuous speech recognition result; a phoneme recognition unit which outputs a second acoustic score as a phoneme recognition result by applying an acoustic model to the speech feature vector; a weight estimation unit which compares the first acoustic score of the continuous speech recognition result of the first search unit with the second acoustic score of the phoneme recognition result of the phoneme recognition unit and, when the first acoustic score of the continuous speech recognition result is better than the second acoustic score of the phoneme recognition result, outputs a first language model weight; and a second search unit which performs a second search by applying a second language model weight, which is the same as the output first language model weight, to the word lattice and outputs a final recognition result.