A vehicle display device includes a display that emits a display image projected on a windshield provided outside as display light, two reflective mirrors that are disposed on a light path of the display light from the display to the windshield and reflect the display light, an optical sensor that detects the external light entering from an opening communicating between the outside and an internal space, and a controller configured to execute temperature decreasing operation of the display for decreasing a temperature thereof when the optical sensor detects the external light. The optical sensor is disposed at a position to which external light directed toward the display via the reflective mirror is reflected by the display to be directed.