11. An apparatus for utterance verification adapted to verify a recognized vocabulary output by a speech recognition device, wherein the recognized vocabulary is obtained by performing speech recognition on a feature vector sequence according to an acoustic model and model vocabulary database, wherein the feature vector sequence comprises feature vectors of a plurality of frames, wherein the acoustic model and model vocabulary database comprises a plurality of model vocabularies, wherein each of the model vocabularies comprises a plurality of states, and wherein the apparatus for utterance verification comprises: a reference score accumulator coupled to the speech recognition device and adapted to calculate an overall maximum reference score according to a log-likelihood score obtained from the speech recognition device by taking a logarithm on a value of a probability of one of the feature vectors of the frames conditioned on one of the states of each model vocabulary, wherein the overall maximum reference score is a summation of the maximum value of log-likelihood scores of the feature vector of each frame conditioned on each state of each of the model vocabularies; a decision device coupled to the reference score accumulator and adapted to calculate a second verification score according to an optimal path score output by the speech recognition device and the overall maximum reference score; a verification score generator coupled to the reference score accumulator and adapted to compare the second verification score with a second predetermined threshold value, so as to reject or accept the recognized vocabulary.
11. An apparatus for utterance verification adapted to verify a recognized vocabulary output by a speech recognition device, wherein the recognized vocabulary is obtained by performing speech recognition on a feature vector sequence according to an acoustic model and model vocabulary database, wherein the feature vector sequence comprises feature vectors of a plurality of frames, wherein the acoustic model and model vocabulary database comprises a plurality of model vocabularies, wherein each of the model vocabularies comprises a plurality of states, and wherein the apparatus for utterance verification comprises: a reference score accumulator coupled to the speech recognition device and adapted to calculate an overall maximum reference score according to a log-likelihood score obtained from the speech recognition device by taking a logarithm on a value of a probability of one of the feature vectors of the frames conditioned on one of the states of each model vocabulary, wherein the overall maximum reference score is a summation of the maximum value of log-likelihood scores of the feature vector of each frame conditioned on each state of each of the model vocabularies; a decision device coupled to the reference score accumulator and adapted to calculate a second verification score according to an optimal path score output by the speech recognition device and the overall maximum reference score; a verification score generator coupled to the reference score accumulator and adapted to compare the second verification score with a second predetermined threshold value, so as to reject or accept the recognized vocabulary. 15. The apparatus for utterance verification as claimed in claim 11 , wherein the reference score accumulator further calculates an overall minimum reference score, wherein the overall minimum reference score is a summation of the minimum value of log-likelihood scores of the feature vector of each frame conditioned on each state of each of the model vocabularies, wherein the verification score generator calculates a fourth verification score according to the optimal path score, the overall maximum reference score and the overall minimum reference score, and wherein the decision device compares the fourth verification score with a fourth predetermined threshold value so as to reject or accept the recognized vocabulary.