A foldable display device and a display apparatus are provided. The foldable display device includes a supporting back plate and a display screen arranged in the front side of the supporting back plate. The supporting back plate includes a first supporting part and a second supporting part, and the first supporting part and the second supporting part may bend towards to the reverse side of the supporting back plate through a folding connection. One end of the display screen is fixedly connected to the first supporting part, and the other end of the display screen is slidably connected to the second supporting part.