Abstract: A lift device having shielded bearings and a strap-like rail that are designed to screw fit in each other. The shielded bearings are mounted in a circumferential thread fashion at a proper pitch on at least three pillars provided inside an outer shell cylinder. A short cylinder has a strap-like rail curvedly wound around its outer circumference so as to screw fit into the bearings. The short cylinder is rotated by a motor mounted on a frame to support the short cylinder at a vertically central position by thrust bearings. Side iron plates are provided on the frame which surround sides of the pillars and the shielded bearings. The iron plates form a cam groove which is slidably engaged on the pillars to stop rotation of the frame around the pillars when the frame moves vertically with the short cylinder, as well as maintaining the short cylinder at the vertically central position.