1. A multi-stage speech recognition apparatus comprising: at least one processor that executes: a first speech recognition unit performing initial speech recognition on a feature vector, which is extracted from an input speech signal, and generating a plurality of candidate words; and a second speech recognition unit rescoring the candidate words, which are provided by the first speech recognition unit, using a temporal posterior feature vector reflected from time-varying voice characteristics and extracted from the feature vector, and outputting a word having a highest score as a final recognition result; wherein the temporal posterior feature vector is a split-temporal context (STC)-TRAP feature vector comprising a left, center, and right context part.