Provided are a document search device, a document search method, a document search system, and a document search program in which, when a document is searched for by using an inputted keyword and a translated keyword, the order of priority of the documents outputted as the result of the search can be adequately determined. A keyword translation means (22) of a document search device (10) translates an inputted keyword to obtain a translated keyword. A keyword score determining means (23) determines a keyword score for each of the inputted keyword and translated keyword. A document search means (24) searches for a document according to the inputted and translated keywords to acquire a plurality of documents. A document score calculating means (25) calculates a document score for each of the search result documents from the keyword scores and the frequency of appearance of each of the keywords. A search result output means (26) places the search result documents in order of document score and performs the output according to the order.
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