A portable information device is provided. The portable information device includes a first chassis and a second chassis, a display, a back part and a movable back plate. The display, which is configured to be foldable in half, is disposed over inner faces of the first and second chassis. The back part, includes a movable hinge configured to join the first and second chassis rotatably. When the first and second chassis are folded towards each other, the movable hinge moves on the inner faces of the chassis in a direction from open ends of the chassis to the back part that is located on an opposite side of the open ends. The movable back plate configured to support a rear face of the display at a part corresponding to the back part. When the first and second chassis are folded towards each other, the movable back plate moves in a direction from the open ends to the back part together with the movable hinge.