There are provided a liquid crystal display device, which positively reflects, by a reflecting electrode and a light-shielding layer, light emitted from a backlight and further reflected from a light-shielding layer or a reflecting layer, and recycles the light while avoiding absorption in a linearly polarizing plate to improve the utilization efficiency of light and thus to realize a bright display screen, and an optical element for use in the liquid crystal display device. The liquid crystal display device comprises: a polarizer for converting light emitted from a back light source to linearly polarized light; a reflecting layer comprising a reflection area part for reflecting the linearly polarized light converted by the polarizer and a transmission area part for transmitting the linearly polarized light converted by the polarizer; and at least one phase difference plate which is disposed so that only the light transmitted through the transmission area part after conversion of the light source-derived light to the linearly polarized light by the polarizer is incident to the phase difference plate.