The invention relates to an automatic pressing device for a steel shaft. A rotating disc system, dual-control button boxes, prepressing systems, pressing systems, a jacking frame, a motor and air cylinder installation frames are installed on a base plate. The motor drives a divider through a synchronous belt. The rotating disc system is provided with feeding and discharging stations and thick and thin steel shaft prepressing stations. A rotating disc is connected with the divider. The thick steel shaft prepressing system is provided with a thick clamping jaw, thick rotating, feeding and prepressing air cylinders and a vibrating disc. The thin steel shaft prepressing system is provided with a thin clamping jaw, thin rotating, feeding and prepressing air cylinders and a vibrating disc. Each steel shaft pressing system is provided with a pressing air cylinder. By using the automatic pressing device, manual feeding is adopted, the rotating disc rotates a station, a gear box enters a prepressing station, the thick clamping jaw clamps a thick steel shaft at a discharge outlet, and the prepressing air cylinder prepresses the thick steel shaft in place; the thin clamping jaw clamps a thin steel shaft at the discharge outlet, and the prepressing air cylinder prepresses the thin steel shaft in place; and the steel shafts enter a steel shaft pressing station, and pressing blocks of the pressing air cylinders press the steel shafts in place. The automatic pressing device is high in efficiency, easy and convenient to operate and high in practicability.