Document retrieval apparatus that accentuates retrieval keyword based on feature index

A document retrieval apparatus is disclosed, including a query character string input unit that accepts an input of query character string including multiple retrieval keywords, a document select unit that selects documents that match the query character string from a document database, a retrieval result output unit that presents retrieval results of the selected documents to a user, and a document output unit that presents the contents of one of the selected documents designated by the user. A feature index that indicates the extent to which each retrieval keyword has contributed to the retrieval for documents is computed. The document output unit determines a manner in which the retrieval keyword is displayed in accordance with the feature index.