1. An apparatus for optimizing a speech recognition result, comprising: a computer that, by using computer executable instructions, receives a speech recognition result from a speech recognition engine, calculates a phoneme acoustic distance between a phoneme sequence of a segment of the speech recognition result and a phoneme sequence of a key word in a keyword list, calculates a tone acoustic distance between a tone sequence of the segment and a tone sequence of the key word, calculates a weighted average of the phoneme acoustic distance and the tone acoustic distance, calculates an average acoustic distance which is obtained by dividing the weighted average by the number of characters, syllables or phonemes of the key word, calculates a language model score of the segment, based on a language model score of each word in the segment, replaces the segment with the key word in a case that the average acoustic distance is lower than a first threshold and the language model score is lower than a second threshold, and outputs the speech recognition result of which the segment is replaced with the keyword to the speech recognition engine.