1. A support device for supporting generation of text from speech data, comprising: a confirmed rate calculator for calculating a confirmed utterance rate which is an utterance rate of a confirmed part having already-confirmed text in the speech data; a candidate obtaining unit for obtaining a plurality of candidate character strings resulting from a speech recognition on an unconfirmed part having unconfirmed text in the speech data; and a selector for selecting one of the plurality of candidate character strings having an utterance time closest to an utterance time of the unconfirmed part in the speech data according to the utterance time consumed to utter the candidate character string at the confirmed utterance rate; further comprising: a candidate time calculator for calculating, for each of the plurality of candidate character strings, an utterance time consumed to utter the candidate character string at the confirmed utterance rate, on the basis of the confirmed utterance rate and a number of moras or syllables in the candidate character string; wherein the confirmed rate calculator calculates, as the confirmed utterance rate, the number of moras or syllables uttered per unit time in the confirmed part having already-confirmed text in the speech data; and wherein the selector preferentially selects one of the plurality of candidate character strings having the utterance time closest to the utterance time of the unconfirmed part in the speech data according to the utterance time calculated by the candidate time calculator; wherein the candidate time calculator comprises: a phoneme string generation unit for generating a phoneme string of the candidate character string; a correction factor calculation unit for calculating a correction factor based on a phoneme string of the candidate character string; and an utterance time calculator for calculating, as an utterance time consumed to utter the candidate character string at the confirmed utterance rate, a value obtained by a calculation where the number of moras in the candidate character string is multiplied by the correction factor and then the obtained value is divided by the confirmation utterance rate.