A portable electronic device includes a flat display, a transparent window, an optical element, an optical zoom lens set and an image sensing element. The flat display includes a display panel with a viewing direction. The transparent window, the optical element, the optical zoom lens set and the image sensing element are all configure in the outer frame of the flat display. The transparent window and the optical element correspond to each other and align in the viewing direction. The optical zoom lens set includes multiple lenses configured at one side of the optical element. The lenses move along a focusing direction to modify the focusing length. The focusing direction is substantially perpendicular to the viewing direction. The image sensing element is configured at one side of the optical zoom lens set, thereby allowing the light to pass through the transparent window, by the optical element guided to the optical zoom lens set, then passing through the lenses, and finally focusing on the image sensing element.