To construct a retrieval formula which is appropriate for retrieving a document matched with a purpose of retrieval even when there exists any peculiar negative example.

This document retrieval method includes: acquiring categories into which positive examples are classified in a document database classified into a plurality of hierarchized categories (step S2); acquiring feature words/phrases included in the positive examples classified into the categories, that is, feature words/phrases not included in negative examples classified into categories as category feature words/phrases for every acquired category (step S4); constructing a sub-retrieval formula based on the categories and the acquired category feature words/phrases for every acquired category (step S5); acquiring the feature words/phrases included in the positive examples (step S3); and constructing a main retrieval formula based on the sum set of the acquired feature words/phrases and the constructed sub-retrieval formula (step S6).