A planar member for forming a hook device includes two side hinge lines and an intermediate hinge line formed in the planar member for forming two side segments and two intermediate segments, and a cut line formed in each of the intermediate segments for separating each intermediate segment into a support portion and a suspension portion, the suspension portions of the intermediate segments are foldable relative to each other and inclined relative to each other and foldable relative to the side segments for forming a three-dimensional suspension hook, the planar member is foldable to a reel for storing and transportation purposes and is quickly folded into the hook device.