The present application discloses a foldable display device, comprising a flexible screen and a support backplane cooperating therewith, the support backplane includes a first support plate and a second support plate hinged therewith by a rotary shaft system; a tension releasing mechanism is disposed at the first support plate or the second support plate, the flexible screen has a first end connected to the first support plate or the second support plate, and a second end opposite thereto, the second end is connected to the tension releasing mechanism, such that the second end of the flexible screen is slidable along a corresponding support plate between a first position in which the foldable display device is in an outward bending state and a second position in which the foldable display device is in a deployed state, and between the second position and a third position in which the foldable display device is in an inward bending state. This foldable display device can prevent the screen from damage as much as possible by providing a tension releasing mechanism.