A portable electronic device is provided, and includes a function key that outputs a predetermined key signal; a key signal regulation unit that regulates a voltage of the predetermined key signal; a Power Management IC (PMIC) that powers on the portable electronic device and identifies a remaining amount of electric power of a battery when receiving the key signal of which a voltage is regulated by the key signal regulation unit in a power-off state; and a controller that controls to perform booting of the electronic device for displaying the remaining amount of electric power of the battery according to the power-on and to display the remaining amount of electric power of the battery.