A portable terminal includes an antenna device having a circuit board on a surface of which a conductive layer is formed, a slit that removes a portion of the conductive layer and extends in a direction, an auxiliary board positioned on the slit to face a surface of the circuit board, and a radiation pattern formed on the auxiliary board, in which the radiation pattern is disposed to partially enclose the slit. Even when the radiation pattern is disposed on the conductive layer, induced current generated around the slit can be controlled in the same direction as signal power, thereby preventing radiation performance from being degraded by an inverse current phenomenon in spite of disposition of the radiation pattern on the conductive layer.