[Challenge] the structure is simplified, the operation provides a convenient Ashi-kan lock structure. The apparatus includes a eccentric cam shaft 10, this by the rotation of the camshaft and a opening cam 20 which is displaced radially outwardly, the eccentric cam shaft is formed a cylindrical neck portion, also, the opening cams The are notch forming a neck portion of the cam shaft is received in the opening cam, via a notch, the lower portion of the eccentric cam shaft is connected to the lower tube 30 of the leg tube, the top and the opening of the eccentric cam shaft cam is fitted to the upper tube 40 of Ashi-kan, opening the cam with respect to the upper tube of Ashi-kan, movably provided in the longitudinal direction of the non-rotatable and top tube around the central axis, also, rotation of the lower tube By the rotation of the camshaft due to an opening cam is pressed against the inner wall of the upper tube is displaced radially outward of Ashi-kan, Ashi-kan locking structure is locked with the upper tube and a lower tube Ashi-kan. .BACKGROUND
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