1. An apparatus for predicting a pleasantness-unpleasantness index of a word using a computer, the apparatus comprising: a computing unit configured to compute an emotion correlation between the word and one or more comparison word, compute emotion correlations between a plurality of reference words included in a reference word set and the one or more comparison word, compute a plurality of first absolute emotion similarity values between the word and the plurality of reference words, and compute at least one second absolute emotion similarity value between a reference word and another reference word for all of the plurality of reference words included in the reference word set; and a prediction unit configured to predict the pleasantness-unpleasantness index of the word by using the plurality of first absolute emotion similarity values, the at least one second absolute emotion similarity value, and a preset pleasantness-unpleasantness index of the plurality of reference words, wherein antonyms of the word are not included in the reference word set, and the computing unit and the prediction unit are embodied on the computer.