Abstract: The adjustable jack mechanism of this invention incorporates a base structure having a support tube, with a plurality of angulated leg supports projecting radially therefrom and which allow pivoting of the support legs to positions parallel with the support tube. A plurality of support legs are pivotally connected to the leg support elements and are stabilized relative to the support tube by a support ring and pivotal support links. An elevation tube is telescopically movable within the support tube and is selectively locked relative thereto by a primary lock including a locking ring that is angulated by an external locking element for frictional gripping relation with the elevation tube. A jack screw is telescopically positioned within the elevation tube and is vertically adjustable by rotation of an adjustment nut for raising or lowering an object support provided at the upper end thereof.