PURPOSE: To prevent a leg body from lateral rattling caused by external force when the leg body is erected.

CONSTITUTION: A leg body 8a is bendably pivotably connected to a leg mounting fitting 4a, and secured fixedly to a frame body 2. When the leg body 8a is erected, a plurality of stopper pieces 11, 11 of an upper hinge body 9 fixed to the leg mounting fitting and a plurality of operating pieces 44 of a lower hinge body 9 fixed to the leg body side are latched holdably to each other. Even if the external force is applied laterally to the leg body, it is caught by a support part and the latch parts at a plurality of spots to prevent rattling.