1. A similarity calculation device for obtaining similarity between a first media data and a text query, the first media data having first meta text including a plurality of words describing contents of the first media data, the similarity calculation device comprising: a single score calculation device which calculates a single score that shows similarity between the text query and a second meta text of a second media data by comparing the text query with the second meta text, the second meta text including a plurality of words describing contents of the second media data; an inter-media similarity calculation device which calculates inter-media similarity that shows similarity between the first meta text of the first media data and the second meta text of the second media data by comparing the plurality of words of the first meta text with the plurality of words of the second meta text; a query similarity calculation device which obtains similarity between the first media data and the text query by using the inter-media similarity and the single score, a meta text creating device which creates meta text including the first meta text and the second meta text based on the first media data and the second media data, respectively, wherein the first meta text includes an error, and the second meta text includes fewer errors than the first meta text; and a query creating difficulty calculation device which calculates a creating difficulty of a text that is same as the text query with the meta text creating device, wherein the query similarity calculation device calculates the similarity between the first media data and the text query by using the inter-media similarity and the single scores of the second media data as well as the creating difficulty, wherein: the meta text creating device creates the meta text by using a dictionary, and the query creating difficulty calculation device calculates the creating difficulty as large, when the text query is an unknown word that is not registered to the dictionary.