An apparatus for raising and lowering a payload, particularly a chair and its user to provide assistance with the sit-to-stand task. The apparatus comprises a base, a platform, linkages attached between base and platform to allow only vertical motion therebetween, an inflatable bag also situated between base and platform, and a source of pressurized fluid such as compressed air, whereby the bag is inflated and deflated to raise and lower the platform. The user may use an existing, favorite chair, including a reclining chair, which is placed upon the platform without modification. In a low position, the platform is quite close to the floor, providing comfort during sitting. In a high position, the platform is greatly elevated, to provide a full measure of sit-to-stand assistance. The apparatus is compact, doesn't interfere with reclining or rocking while sitting, and is easily deployable, movable, and storable.