A head-mounted display device comprising: a front element adapted to be placed or be installed with a display device; and a pair of extending portions respectively connected to two opposite ends of the front element; an adjustable fixing assembly, two opposite ends of the adjustable fixing assembly being slidably disposed at the pair of extending portions, wherein the adjustable fixing assembly is adapted to be subjected to an external force to move in a first sliding direction away from the front element, and when the external force is removed from the adjustable fixing assembly that has been moved in the first sliding direction, the adjustable fixing assembly is adapted to move in a second sliding direction opposite to the first sliding direction; wherein the adjustable fixing assembly comprises: a frame; and a pair of connection members respectively connected to two opposite ends of the frame, and the pair of connection members being slidably disposed on the pair of extending portions; and characterized by that each of the extending portions comprises a slide groove, and the adjustable fixing assembly comprises: a sliding member fixed to the connection member and slidably disposed in the slide groove; a first fixing portion disposed in the slide groove; a second fixing portion disposed on the sliding member; and a plurality of restoring members providing a pull force, two opposite ends of each restoring member being respectively fixed to the first fixing portion and the second fixing portion; and wherein each of the extending portions has a first end and a second end opposite to each other, the second end comprises a first stop portion, the sliding member comprises a second stop portion corresponding to the first stop portion, and the second stop portion is adapted to reciprocatingly slide between the first end and the second end. a front element adapted to be placed or be installed with a display device; and a pair of extending portions respectively connected to two opposite ends of the front element; an adjustable fixing assembly, two opposite ends of the adjustable fixing assembly being slidably disposed at the pair of extending portions, wherein the adjustable fixing assembly is adapted to be subjected to an external force to move in a first sliding direction away from the front element, and when the external force is removed from the adjustable fixing assembly that has been moved in the first sliding direction, the adjustable fixing assembly is adapted to move in a second sliding direction opposite to the first sliding direction; wherein the adjustable fixing assembly comprises: a frame; and a pair of connection members respectively connected to two opposite ends of the frame, and the pair of connection members being slidably disposed on the pair of extending portions; and a frame; and a pair of connection members respectively connected to two opposite ends of the frame, and the pair of connection members being slidably disposed on the pair of extending portions; and characterized by that each of the extending portions comprises a slide groove, and the adjustable fixing assembly comprises: a sliding member fixed to the connection member and slidably disposed in the slide groove; a first fixing portion disposed in the slide groove; a second fixing portion disposed on the sliding member; and a plurality of restoring members providing a pull force, two opposite ends of each restoring member being respectively fixed to the first fixing portion and the second fixing portion; and a sliding member fixed to the connection member and slidably disposed in the slide groove; a first fixing portion disposed in the slide groove; a second fixing portion disposed on the sliding member; and a plurality of restoring members providing a pull force, two opposite ends of each restoring member being respectively fixed to the first fixing portion and the second fixing portion; and wherein each of the extending portions has a first end and a second end opposite to each other, the second end comprises a first stop portion, the sliding member comprises a second stop portion corresponding to the first stop portion, and the second stop portion is adapted to reciprocatingly slide between the first end and the second end.