Disclosed is a transparent display device in which the total refection efficiency of a light guide plate supplying light to a liquid crystal display panel is enhanced thereby enhancing luminance in the image mode, and the transparent display device may include a liquid crystal display panel; a light source disposed at one side of a lower portion of the liquid crystal display panel to emit light; a first polarizing plate for polarizing the light emitted from the light source; a light guide plate disposed at a lower portion of the liquid crystal display panel to totally reflect the light polarized to an axis by the first polarizing plate to a lateral surface thereof and supply to the liquid crystal display panel, and transmit natural light entered from a lower direction therethrough; a plurality of air layers formed inside the light guide plate to totally reflect incident light; and a second polarizing plate disposed at an upper portion of the liquid crystal display panel to control the amount of polarized light transmitting the liquid crystal display panel.