Abstract: This invention is directed to a wheel-mounted portable jack which is capable of lifting large objects from a minimum ground clearance to a considerable height without resetting. The structure of the jack includes an upper member and a lower frame member pivotally attached together and movable between a normally contracted position and an expanded position under the control of lift means extending between a base and the upper frame. The lift means is operative to actuate the frame members simultaneously to advance from a collapsed or closed position in which the frame members are in parallel, horizontal relation to each other to an extended or open position in which the frame members approach a vertical, straight line relation to each other resembling the opening of a set of jaws. The jack includes a self-contained power source, drive means, and control apparatus as well as an apparatus for lifting the rear end of the jack for alignment purposes, a handle, and wheels for convenience in transporting the jack.