A lifting device (500, 500') comprising: a plurality of vertical support structures, each of which includes a half tube having an inner surface defining a receiving space and formed with a thread unit, and a mounting member connected to an outersurface of said half tube, said thread unit including a series of axially spaced-apart helical groove halves; a plurality of rotation units, each of which is disposed in said receiving space and is movable along the length of said half tube, each of said rotation units being rotatably and threadedly engaged to said thread unit of said half tube of a respective one of said vertical support structures; a plurality of slide housings respectively receiving said rotation units and respectively slidable relative to said half tubes of said vertical support structures to move upward and downward; a lift carrier having a carrier frame structure disposed between said vertical support structures, said carrierframe structure including a plurality of connecting end portions connected to and riding on said slide housings, respectively; a drive motor connected to said carrier frame structure; and a plurality of transmission units, each of which is connected between said drive motor and a respective one of said rotation units; wherein when said drive motor is operated, said transmission units respectively drive said rotation units to rotate and move upward and downward along said helical groove halves in said half tubes of said vertical support structures simultaneously; wherein said half tube further has two tube flanges projecting outwardly and radially from two radially opposite ends of said half tube and extending along the length of said half tube; and wherein each of said slide housings is substantially cylindrical, and has two housing flanges that project outwardly and radially from two radially opposite ends of a corresponding one of said slide housings and that are slidable along said tube flanges, and two slide bars are respectively connected to said housing flanges and slidably engaged to said tube flanges, whereby each of said rotation units includes a rotating block having an outer surface formed with a helical groove, a plurality of bearing balls received in said helical groove and engaged to said thread unit, a rotating shaft extending through said rotating block, and a driven sprocket mounted on said rotating shaft, said drive motor having a motor shaft, each of said transmission units including a drive sprocket mounted on said motor shaft, and a drive chain trained between said drive sprocket of one of said transmission units and said driven sprocket of the respective said rotation unit. a plurality of vertical support structures, each of which includes a half tube having an inner surface defining a receiving space and formed with a thread unit, and a mounting member connected to an outersurface of said half tube, said thread unit including a series of axially spaced-apart helical groove halves; a plurality of rotation units, each of which is disposed in said receiving space and is movable along the length of said half tube, each of said rotation units being rotatably and threadedly engaged to said thread unit of said half tube of a respective one of said vertical support structures; a plurality of slide housings respectively receiving said rotation units and respectively slidable relative to said half tubes of said vertical support structures to move upward and downward; a lift carrier having a carrier frame structure disposed between said vertical support structures, said carrierframe structure including a plurality of connecting end portions connected to and riding on said slide housings, respectively; a drive motor connected to said carrier frame structure; and a plurality of transmission units, each of which is connected between said drive motor and a respective one of said rotation units; wherein when said drive motor is operated, said transmission units respectively drive said rotation units to rotate and move upward and downward along said helical groove halves in said half tubes of said vertical support structures simultaneously; wherein said half tube further has two tube flanges projecting outwardly and radially from two radially opposite ends of said half tube and extending along the length of said half tube; and wherein each of said slide housings is substantially cylindrical, and has two housing flanges that project outwardly and radially from two radially opposite ends of a corresponding one of said slide housings and that are slidable along said tube flanges, and two slide bars are respectively connected to said housing flanges and slidably engaged to said tube flanges, whereby each of said rotation units includes a rotating block having an outer surface formed with a helical groove, a plurality of bearing balls received in said helical groove and engaged to said thread unit, a rotating shaft extending through said rotating block, and a driven sprocket mounted on said rotating shaft, said drive motor having a motor shaft, each of said transmission units including a drive sprocket mounted on said motor shaft, and a drive chain trained between said drive sprocket of one of said transmission units and said driven sprocket of the respective said rotation unit.