An encrypted file is constituted by an assemblage of records having a plurality of items, and at least key items among the plurality of items that are keys in a retrieval are encrypted. The expansion means of a retrieval device decrypts at least key items of each record of the encrypted file, attaches identifiers that indicate which records the key items belong to, and expands the decrypted key items and identifiers in a work area of a main memory. A retrieval means retrieves from the work area key items that satisfy retrieval conditions that are applied by the user, reads the appropriate original records from the encrypted file if retrieval succeeds, decrypts the records, and presents them to the user.