24. A non-transitory computer-readable recoding medium that stores a program which causes a computer to execute the processes of: receiving a recognition result and a target word string which is specified in the recognition result; generating an alternative candidate word string in a position of the target word string; training a classifier which is configured to discriminate between the target word string and the alternative candidate word string; extracting a feature value representing an adjacent context in the position of the target word string; 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.
24. A non-transitory computer-readable recoding medium that stores a program which causes a computer to execute the processes of: receiving a recognition result and a target word string which is specified in the recognition result; generating an alternative candidate word string in a position of the target word string; training a classifier which is configured to discriminate between the target word string and the alternative candidate word string; extracting a feature value representing an adjacent context in the position of the target word string; 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. 34. The recording medium according to claim 24 , wherein the program further causes the computer to execute the processes of: executing the processes of the generating, the training, the extracting and the classifying determining to obtain a confidence measure of the target word string and a confidence measure of the alternative candidate word string, and outputting a word string having a largest confidence measure.