Vehicle-mounted display device, seat assembly and vehicle

The utility model discloses a vehicle-mounted display device, a seat assembly and a vehicle, the vehicle-mounted display device comprises a support suitable for being installed on the back face of a seat; the display screen is rotatably connected with the support, and the rotating axis of the display screen extends in the horizontal direction; wherein the side length, perpendicular to the rotating axis, of the display screen is A, and when the display screen rotates to the vertical direction, the distance between the horizontal line equally dividing the display screen in the vertical direction and the orthographic projection, in the plane where the display screen is located, of the rotating axis of the display screen is not larger than 10% A. According to the embodiment of the utility model, the vehicle-mounted display equipment is not easy to swing, has high position stability, and is beneficial for passengers to watch and operate.