It is an object of the present invention to provide encryption and decryption apparatuses capable of selecting a part of file portions handled on a computer, and encrypting and decrypting only the thus selected part of file portions. The encryption apparatus 200 and the decryption apparatus 300 can encrypt and decrypt all of item data elements in item data portions in specified association with a specific item name portion of the database 400 while maintaining reciprocal relationships among the item data portions in the database 400 regardless of whether item data elements in the item data portions are encrypted or not. This leads to the fact that major features of the database such as data search and data alignment functions remain enabled even if item data elements in item data portions of the database are encrypted.