Encryption methods allowing encrypted data to be stored in a database and processed in the encrypted state have been proposed. However, since it is necessary for an application to use plaintext data, usage is only possible where security is assured. When an application for processing encrypted data stored in a database is used from a user system, the application is launched from the user system via an application extension unit. When the application processes the encrypted data stored in the database, the application extension unit performs a process in which, if an encryption SQL function enabling the encrypted data stored in the database to be processed is registered, the SQL function enabling the function for processing plaintext is replaced with the encryption SQL function, and, if a substitution process is registered, the SQL function is replaced with a substitution process function enabling the substitution process to be performed. It is thereby made possible to process data, without decryption, in a location at which security is not assured.