To allow to avoid the interference with a working board in the using time, while to prevent to disturb the other works in the non-using time.

While an undulating arm 12 is pivoted allowable to undulate to a rotary board 11, an extension boom 13 is pivoted to the tip of the undulating arm 12, and an extension cylinder 16 is provided between the undulating arm 12 and the extension boom 13. When a lifting device 10 is used, the extension boom 13 is extended and contracted at a little upper side than the horizontal direction by extending the extension cylinder 16 as well as erecting the undulating arm 12, and thereby, the interference between the extension boom 13 and a working board 7 is avoided. On the other hand, when the lifting device 10 is not used, the undulating arm 12 is made fall down to the outer side, and the extension boom 13 is superposed on the undulating arm 1 in the contracting condition, and stored.