PURPOSE: To simplify the structure by providing an upper and a lower parallel pole shafts in stairs, and respectively connecting both upper and lower ends thereof to both upstairs and downstairs ball screw, and respectively connecting both upstairs and downstairs ball screws to an orthogonally crossing shaft reduction gears motor through plural orthogonally crossing shaft converters.

CONSTITUTION: Both an upper and a lower pole shafts 1, 2 are providing in stairs. Each upstairs end 1', 2' of both the upper and lower shafts 1, 2 are respectively connected to both an upper and a lower ball screw nuts 4, 5 of an upstairs ball screw 3. Each downstairs end 1", 2" of both the upper and the lower parallel pole shafts 1, 2 are respectively connected to both an upper and a lower ball screw nuts 7, 8 of a downstairs ball screw 6. Furthermore, both the upstairs and downstairs ball screws 3, 6 are respectively connected to an orthogonally crossing shaft of an orthogonally crossing shaft reduction gears motor 11 through plural orthogonally crossing shaft converters 9, 10. Step plates of a stairs are alternately connected to both the upper and lower parallel pole shafts 3, 6, and while, the orthogonally crossing shaft reduction gears motor 11 is normally and reversely rotated to elevate and lower the step plates.