1. A query processing system by query transformation, which processes a query when a user requests the query based on an original database structure from a database management system managing a database with at least a column encrypted, the system comprising: a name mapping table storing a field name corresponding to a column to be encrypted and a table name including the column in an encryption-related table of the database management system, by pairing an original name and an encrypted name; a packet processing unit for capturing a query that the user requests from the database management system, transmitting a transformed query to the database management system and receiving a result value of the query processed by the database management system; a query transforming unit for analyzing and transforming the query captured by the packet processing unit into a query capable of referencing an encrypted database by converting an encryption-related item using the name mapping table or encrypting the encryption-related item using an encryption processing unit; a result value transforming unit for transforming the result value, processed using the query transformed by the database management system, into a result value corresponding to the original database by converting an encryption-related item therein using the name mapping table 440 or decrypting the encryption-related item using the encryption processing unit; and the encryption processing unit for encrypting an encryption-related item when the query transforming unit calls and decrypting an encryption-related item when the result value transforming unit calls.