8. The method according to claim 6 , further comprising: a probability storage unit configured to store the forward probabilities of the final state for said one of continuous phrase segments, which is obtained by the first decoding step, and the final state for the trailing phrase segment, which is obtained by the second decoding step, by associating with number of the states up to the final state and with frame number up to current one of the frame; and a speech feature storage unit configured to store the sequence of trailing speech features for the respective frames by associating with the frame numbers, wherein the third decoding step obtains the forward probabilities of the respective states of the state transition models for the stored sequence of trailing speech features by referring to the transferred trailing grammar segments, the stored forward probabilities of the final states, the number of the states and the frame numbers.
8. The method according to claim 6 , further comprising: a probability storage unit configured to store the forward probabilities of the final state for said one of continuous phrase segments, which is obtained by the first decoding step, and the final state for the trailing phrase segment, which is obtained by the second decoding step, by associating with number of the states up to the final state and with frame number up to current one of the frame; and a speech feature storage unit configured to store the sequence of trailing speech features for the respective frames by associating with the frame numbers, wherein the third decoding step obtains the forward probabilities of the respective states of the state transition models for the stored sequence of trailing speech features by referring to the transferred trailing grammar segments, the stored forward probabilities of the final states, the number of the states and the frame numbers. 9. The method according to claim 8 , wherein the grammar transferring step stops the transfer of the trailing grammar segments when the transfer is not completed even when a predetermined time is elapsed.