A mirror display device, which includes: a display panel; a first polarizer disposed on the display panel; and an optical structure disposed on the first polarizer. The optical structure includes: a first polarization conversion layer; and a second polarization conversion layer or a reflection layer, wherein the first polarization conversion layer is disposed between the first polarizer and the second polarization conversion layer or the reflection layer; wherein a sum of a first reflectance and a first transmittance of the optical structure is greater than 100% and less than 150%, in which the first reflectance is referred to a percentage of external light irradiating into the mirror display device and reflected by the optical structure, and the first transmittance is referred to a percentage of light passing through a first polarizer and then irradiating into and passing through the optical structure.