1. An apparatus for predicting a pleasantness-unpleasantness index of a word, 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.