A portable electronic device includes an audio port, a universal serial bus (USB) circuit, an audio circuit, a detecting unit, a switch, and a microcontroller. The detecting unit is connected to the audio port. The detecting unit generates a detecting signal in response to detection of either the earphone/microphone or the USB apparatus being connected to the audio port. The microcontroller is connected to the detecting unit and the switch. The microcontroller selects the audio circuit or the USB circuit to the audio port by the switch according to the detecting signal.