A word extraction unit 11 that analyzes m texts to extract n words, a vector computation unit 12 that converts each of the m texts into a q-dimension vector and each of the n words into a q-dimension vector, thereby computing m text vectors including q axis components and n word vectors including q axis components, and an index value computation unit 13 that takes each of inner products of the m text vectors and the n word vectors, thereby computing a similarity index value reflecting a relationship between the m texts and the n words are included, and it is possible to obtain a similarity index value representing which word contributes to which text and to what extent as an inner product value by calculating an inner product of a text vector computed from a text and a word vector computed from a word included in the text.