A transparent display device is provided herein, which comprises a display module and a backlight module. The display module includes a liquid crystal display panel, polarizers and an optical film. The backlight module includes a light source and a light guide plate, wherein the light guide plate includes a first light incident plane, a second light incident plane and a light emitting plane. The first light incident plane is disposed opposite to a light emitting plane of the light source. A plurality of caves are disposed on the second light incident plane to enhance the environmental light. The present invention raises an incident amount of the environmental light.