A lifting device includes a guide unit, a support unit and a lifting unit. The guide unit is extendable and retractable along a direction. The support unit is disposed in the guide unit and includes a securing connector fixed to a seat body and made of elastic material, a support tube connected to the securing connector, and a support member disposed on the support tube. The lifting unit includes a first rod-actuating screw member disposed on the support member and having a first threaded hole, and a threaded rod unit including a first threaded rod extending into the support tube and being threadedly engaged with the first threaded hole, such that the first threaded rod is rotatable by an external force and movable in the direction.