1. A speech-recognition device which acquires an internal recognition result from its recognition processing of input speech data and an external recognition result from recognition processing of said input speech data by one or more external recognizer that exists outside, to thereby determine a final recognition result, the speech-recognition device comprising: an acoustic model in which feature quantities of speeches are modelized; a language model in which notations and readings of more than one recognition-object words of the speech-recognition device are stored; a reading dictionary in which pairs of notations and readings of the recognition-object words and other words than the recognition-object words are stored; an analyzer that analyzes the input speech data to calculate a feature vector; an internal recognizer that performs, using the acoustic model, pattern collation between the feature vector calculated by the analyzer and each of words stored in the language model to thereby calculate their respective acoustic likelihoods, followed by outputting, as the internal recognition result, the notations, the readings and the acoustic likelihoods of top one or more high-ranking words in the acoustic likelihoods; a reading-addition processor that acquires the external recognition result from recognition processing of the input speech data by the external recognizer, adds a reading for said external recognition result by use of the reading dictionary, and outputs a reading-added result composed of said external recognition result and the reading therefor; a re-collation processor that performs, using the acoustic model, pattern collation between the feature vector calculated by the analyzer and the reading-added result outputted by the reading-addition processor, to thereby calculate an acoustic likelihood for the external recognition result; and a result-determination processor that compares the acoustic likelihoods of the internal recognition result with the acoustic likelihood of the external recognition result, to thereby determine the final recognition result.