Disclosed herein is an antenna device for use with a portable wireless terminal having a main body, and a sub-body slidably coupled thereto, with a first antenna mounted in the main body and a second antenna mounted on the sub-body. The second antenna is selectively exposed to the outside as the sub-body moves slidingly on the main body. Conventional sliding-type terminals incorporate an antenna device in its main body that is interfered with by user body parts, thereby causing deteriorated performance. The antenna device of the present invention improves performance by using an additional second antenna mounted on the sub-body of the terminal to improve transmitting/receiving signal quality of the terminal. Furthermore, as such an antenna device is incorporated inside a sliding-type terminal or a pop-up type terminal, it is possible to eliminate risk of damage and to diversify the design of the terminal.