12. A confidence measure calculation apparatus that calculates a confidence measure of a target word string specified in a recognition result, the apparatus comprising: a generator generating an alternative candidate word string in a position of the target word string; a training unit training a classifier which is configured to discriminate between the target word string and the alternative candidate word string; an extractor extracting a feature value representing an adjacent context in the position of the target word string; and a calculator determining whether a true word string in the position of the target word string is the target word string or the alternative candidate word string by using the classifier and the feature value, and calculating a confidence measure of the target word string on the basis of the determination result.
12. A confidence measure calculation apparatus that calculates a confidence measure of a target word string specified in a recognition result, the apparatus comprising: a generator generating an alternative candidate word string in a position of the target word string; a training unit training a classifier which is configured to discriminate between the target word string and the alternative candidate word string; an extractor extracting a feature value representing an adjacent context in the position of the target word string; and a calculator determining whether a true word string in the position of the target word string is the target word string or the alternative candidate word string by using the classifier and the feature value, and calculating a confidence measure of the target word string on the basis of the determination result. 18. The apparatus according to claim 12 , wherein the generator refers to an inter-word confusion matrix to generate, as the alternative candidate word string, a word string that a recognition system tends to confuse with the target word string.