To facilitate a folding operation and an unlocking operation of support legs, minimize abrasion between a lever and a support rod by leveling the cross section of the circumferential edge of the lock lever, prevent the rattling when sliding the support rod, improve the locking property and the robustness, and easily and inexpensively manufacture.

A rail 4 having a passage 3 for sliding a support rod top part 2 in a space toward a top board 1 is formed into a U-shaped cross section. Both ends of the passage 3 are formed with first and second locking parts 5 and 5' of the support rod top part 2. A lever 6 of U-shaped cross section is externally fitted around the outward end adjacency of the rail 4 and turnably attached thereto. The lever 6 is constantly energized in the closing direction. Oblique edges rejected by the support rod top part 2 are formed into projecting arc shapes from the respective inward edges of the both side plates 60 and 60 of the lever 6. Recessed groove parts 62 and 62 of the support top part 2 are recessedly formed in positions continuing to the projecting arc parts 61 and 61 and corresponding to a first locking part 5. A pushing piece 64 is formed by extending the outer end of the lower face plate 63 of the lever 6.

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