Provided is a method for folding a foldable display device, in which the foldable display device includes a base panel plate, wherein a second panel plate hinged to one side of the base panel plate is folded, and a first panel plate hinged to the other side of the base panel plate is folded, and the first and second panel plates are unfolded, so that portions of a display panel, which are repeatedly folded and unfolded, can be stably supported, the display panel can be prevented from being damaged, and a thickness of the foldable display device can be thinner than a foldable smartphone folded once so that a volume thereof can be minimized, thereby providing a display panel that becomes wider when the first and second panel plates are unfolded.