There is provided an antenna for tuning a resonant frequency. The antenna includes a first and a second arms connected to the antenna feeding portion at a common end thereof. The second arm has each of the plurality of branches including a switch for selecting a length of an electrical loop formed by the second arm and an end of a ground plane, each of the switches is connected to the ground plane. A first resonant frequency performed by the first arm is higher than a second resonant frequency by the second arm when each of the switches is open, and the first resonant frequency is lower than a third resonant frequency by the second arm when one of the switches is selected to connect the second arm and the ground plane so that the length of the electrical loop is maximum.