The present invention relates to a portable electronic device including a backlight module having a first light output surface toward a foreside and a second light output surface opposite to the first light output surface and toward a rear side, and providing a first surface light source and a second surface light source through the first light output surface and the second light output surface respectively; a lightening unit configured in proximity to the first light output surface and lightened by receiving the first surface light source; and a lightening pattern layer configured in proximity to the second light output surface, receiving the second surface light source and including a mask part and a light-transmittable part formed with a mark pattern, wherein the second surface light source is masked by the mask part and passes through the light-transmittable part whereby the mark pattern is accordingly lightened and defined.