4. The apparatus of claim 3 , wherein the computing unit computes a relative emotion similarity value between the word and each the plurality of reference words (a plurality of relative emotion similarity values) by using the plurality of first absolute emotion similarity values and the at least one second absolute emotion similarity value, and the prediction unit predicts the pleasantness-unpleasantness index of the word by using the plurality of relative emotion similarity values and the pleasantness-unpleasantness index of the plurality of reference words, and an i-th relative emotion similarity value from among the plurality of relative emotion similarity values is computed using an i-th first absolute emotion similarity value between the word and an i-th reference word from among the plurality of reference words and second absolute emotion similarity values between the i-th reference word and the reference words of the reference word set other than the i-th reference word.
5. The apparatus of claim 4 , wherein the computing unit computes the i-th relative emotion similarity value by using an equation shown below: relative_similarity ⁢ ⁢ ( A → , B ι → ) = similarity ⁢ ⁢ ( A → , B ι → ) - ∑ B j ∈ S ⁢ similarity ⁢ ⁢ ( B ι → , B J → )  S  where {right arrow over (A)} is a first vector, {right arrow over (B ι )} is a second vector of an i-th reference word from among the plurality of reference words, S is the reference word set, relative_similarity({right arrow over (A)}, {right arrow over (B ι )}) is the i-th relative emotion similarity value, similarity ({right arrow over (A)}, {right arrow over (B ι )}) is the i-th first absolute emotion similarity value, ∑ B j ∈ S ⁢ similarity ⁢ ⁢ ( B ι → , B J → )  S  is the second absolute emotion similarity values between the i-th reference word and the other reference words of the reference word set, and |S| is a size of the reference word set.