A lifting device including a body, a sliding member, a pulley, a worm, an elastic member and a connecting member is provided. The sliding member is used to set an object and stays at any position between two positions. The pulley has a fist groove. A curvature radius of the first groove is a constant value. The worm has a second groove. A curvature radius of the second groove is a non-constant value. The elastic member is disposed in the body. When the sliding member is slid between the two positions, the pulley and the worm are rotated in at least one circle. A sum which a first torque generated by a gravity of the object and the sliding member with the curvature radius of the first groove and a second torque generated by a force of the elastic member with the curvature radius of the second groove is zero.