To provide a supporting device which allows fixing of objects to be fixed on shaft work simply, quickly and in safety.

In the supporting device 1 for an object to be fixed such as a door 6 or a window sash as used when fixing the object to be fixed on the shaft work 5 arranged on a pair of parallel conveyors 4 from below it 5, there are included a slide arm 2 which is disposed on one side of the conveyors 4 and has a horizontal plane lower than the conveyors 4 rotatable on the fulcrum at a point in the vicinity of the side and a lifting cylinder 3 which is made slidable to a desired position of the slide arm 2 while having a support surface thereof liftable or lowerable.