A similarity search apparatus (20,30) comprising a similarity index value computation apparatus and a similar text search unit (23,33), the similarity index value computation apparatus comprising: a word extraction unit that analyzes m - where m>=2-texts and extracts n - where n>=2-words from the m texts; a text vector computation unit that converts each of the m texts into a q-dimension vector - where q>=2 according to a predetermined rule, thereby computing m text vectors including q axis components; a word vector computation unit that converts each of the n words into a q-dimension vector according to a predetermined rule, thereby computing n word vectors including q axis components; characterised by an index value computation unit that takes a product of a text matrix having q axis components of each of the m text vectors as respective elements and the transpose of a word matrix having q axis components of each of the n word vectors as respective elements, thereby computing an index value matrix having m × n similarity index values reflecting a relationship between the m texts and the n words as respective elements, wherein the similar text search unit (23,33) sets m - 1 other texts except for one of the m texts as search targets when the one text is designated as a search key from the m texts, determines a similarity between a search key-related text index value group including n similarity index values related to the one text and a search target-related text index value group including n similarity index values related to each of the m - 1 other texts, and extracts a predetermined number of texts from the m - 1 other texts as search results in descending order of the similarity. a word extraction unit that analyzes m - where m>=2-texts and extracts n - where n>=2-words from the m texts; a text vector computation unit that converts each of the m texts into a q-dimension vector - where q>=2 according to a predetermined rule, thereby computing m text vectors including q axis components; a word vector computation unit that converts each of the n words into a q-dimension vector according to a predetermined rule, thereby computing n word vectors including q axis components; characterised by an index value computation unit that takes a product of a text matrix having q axis components of each of the m text vectors as respective elements and the transpose of a word matrix having q axis components of each of the n word vectors as respective elements, thereby computing an index value matrix having m × n similarity index values reflecting a relationship between the m texts and the n words as respective elements, wherein the similar text search unit (23,33) sets m - 1 other texts except for one of the m texts as search targets when the one text is designated as a search key from the m texts, determines a similarity between a search key-related text index value group including n similarity index values related to the one text and a search target-related text index value group including n similarity index values related to each of the m - 1 other texts, and extracts a predetermined number of texts from the m - 1 other texts as search results in descending order of the similarity.