Abstract: Apparatus is disclosed for elevating a platform of the type adapted to carry workers, tools, equipment and/or material. Parallelogram boom assemblies support the platform from a mobile frame such that the platform can be raised and lowered in a level attitude. Each boom assembly comprises a compression arm and a tension arm. The two boom assemblies are interconnected by means of a floating frame and a rigid tension member which is arranged to raise and lower the upper boom assembly relative to the floating frame as the lower boom assembly is raised and lowered, respectively, relative to the mobile frame. In one embodiment the upper and lower boom assemblies lie in a horizontal orientation when in their retracted mode. In another embodiment an upstanding support carries the lower boom assembly which inclines downwardly in the retracted position and connects through a floating frame with an upper boom assembly which is formed with a zigzag shape.