To arbitrarily adjust driving force for rising and falling an upper half body supporting frame.

When a rod 62 is actuated and projected from a cylinder main body 61 by the supply of a gas pressure to a gas lifter 60 from the state that an upper half body supporting frame 20 is almost horizontal, since a driving frame 50 performs an erecting operation around a movable supporting shaft 41 as a center and the free end 52 pushes up the back surface part of the upper half body supporting frame 20 through a roller 52a, the upper half body supporting frame 20 is erected around a hip part supporting shaft 11 as the center. At this time, by changing the fixed position of a movable pedestal 40 by the operation of a shift lever 80, since the moment of force is changed by a distance between a pressurizing supporting position through the driving frame 50 to which the energizing force of the gas lifter 60 acts and the hip part supporting shaft 11, supporting force to the upper half body supporting frame 20 can be arbitrarily adjusted.