An object is to provide a liquid crystal display device which can recognize image display even when the liquid crystal display device is used in a dim environment. In one pixel, a pixel electrode including both of a region where incident light through a liquid crystal layer is reflected and a transmissive region is provided, and image display can be performed in both modes: the reflective mode where external light is used as an illumination light source; and the transmissive mode where the backlight is used as an illumination light source. When there is external light with insufficient brightness, that is, in a dim environment, the backlight emits weak light and an image is displayed in the reflective mode, whereby image display can be performed.