1. A document retrieval system, comprising: a document database for storing data on a plurality of documents; indices used for indexing numeric values and texts in each of the documents stored in the document database, each of the indices used for indexing the text being a group of a term constituting the text and a frequency of the term in the document, each of the indices used for indexing the numeric value being a group of a label describing a feature represented by the numeric value, an interval including the numeric value, and a frequency of the numeric value in the document; and an arithmetic unit for receiving a designation of a document as a retrieval input, calculating a similarity between the designated document and each of the documents stored in the document database by use of the indices, and presenting the documents in order of similarity.