Data security device and method and mobile terminal including the same

A data security apparatus and a mobile terminal having the same are provided to overcome a restricted capacity of a smart card by using a large-capacity flash memory and storing security algorithm of the smart card in a memory. An I/O terminal(210) is electrically connected to a mobile communication terminal. A first storage unit(220) stores a security program, which encodes and decodes data. A controller receives a data encoding request signal from the mobile communication terminal through the I/O terminal and encodes the data by using the security program. The controller receives a data decoding request signal from the mobile communication terminal through the I/O terminal and decodes the encoded data by using the security program. A second storage unit(300) stores the encoded data from the controller. A capacity of the second storage unit is greater than that of the first storage unit.