A portable electronic device having a display screen capable of changing display directions is disclosed. The portable electronic device, such as a tablet personal computer, includes a tiltmeter, a display direction determining circuit and a display direction changing circuit. The tiltmeter measures a first tilt angle of a first axis of a display screen of the portable electronic device with respect to a horizontal plane, and measures a second tilt angle of a second axis of the display screen of the portable electronic device with respect to the horizontal plane. The display direction determining circuit determines whether or not a display direction of the display screen is to be changed based on the changing conditions generated by the first tilt angle and the second tilt angle as measured by the tiltmeter. The display direction changing circuit changes the display direction of the display screen from a current display direction to a different display direction according to a determination result formed by the display direction determining circuit.