One or more pantographs are connected below a working base and are connected with a main cylinder horizontal or inclined in respect to a supporting base so as to be driven to be extended or contracted. One or more comparatively short auxiliary telescopic cylinders are erected below the working base. During the initial phase of upward movement of the working base the auxiliary cylinders will act directly to push up the working base and, when it has been elevated to a predetermined height, the pushing force is shifted to the main cylinder so that the working base may be further elevated through the pantographs.When the working base is lowered, the pantographs and main cylinder will be compactly folded.