Disclosed is an antenna device for a portable terminal, including a circuit board having a conductive layer attached on a surface, a first slit formed by partially removing the conductive layer in a position adjacent to one side of the circuit board, the first slit extending in parallel with a lateral periphery of the circuit board, a radiation portion comprising part of the conductive layer positioned on the lateral periphery of the circuit board in one side of the first slit, and a feed line placed on the first slit and adapted to feed the radiation portion from the other side of the first slit. The radiation portion further comprises a second slit extending from the first slit to the lateral periphery of the circuit board across part of the conductive layer forming the radiation portion, and a frequency adjustment element placed on the second slit.