A portable electronic device is provided having a foldable housing, a flexible display, and a hinge structure. The hinge structure includes a hinge cover, a rotary shaft assembly substantially accommodated in the hinge cover under the flexible display, and including a first rotary shaft and a second rotary shaft substantially parallel to each other. The hinge structure also includes a first arm structure and a second arm structure rotatably coupled with the first rotary shaft and the second rotary shaft, respectively. The hinge structure further includes a guide member connected with the rotary shaft assembly and including a recessed area located substantially between the first rotary shaft and the second rotary shaft when viewed from above the flexible display. The recessed area is configured to accommodate at least part of a third display portion when the foldable housing is at least partially folded.