1. An apparatus for recognizing voice, comprising: a feature vector extraction unit dividing an input voice signal into predetermined unit regions, and extracting feature vectors corresponding to each of the unit regions; a predicted node extraction unit extracting a list of second nodes whose travels to a first node corresponding to the extracted feature vectors are predicted, with reference to a network of one or more nodes; a probability distribution generation unit converting respective multiple waveform probability distributions, which constitute the voice signals corresponding to each of the second nodes, into single waveform probability distributions, grouping the single waveform probability distributions according to degree of similarity there between, and generating representative single waveform probability distributions that represent each probability distribution group; a single waveform similarity calculation unit calculating degrees of single waveform similarity of the first node and each probability distribution group by substituting the extracted feature vectors into the representative single waveform probability distributions; a multiple waveform similarity calculation unit calculating degrees of multiple waveform similarity by substituting the extracted feature vectors into each of the multiple waveform probability distributions that constitute the representative single waveform probability distributions usable to calculate the degrees of single waveform similarity in a preset range; and an output unit outputting a function-performing signal corresponding to a multiple waveform probability distribution that enables calculation of a highest of the calculated degrees of multiple waveform similarity only when a number of operations for calculating the degrees of the multiple waveform similarity is smaller than a preset threshold or outputting an unregistered word.