in the hole 62 the elastic body 63 can perform elastic displacement toward the outside from the hole 62 the elastic body 63 then moves back and forth through the hole 62 at a direction d by the elastic force of the elastic body 63 per se and by the pressing force of the interior wall of the first supporting cylinder 501 pressing the elastic body 63 as shown in fig6 because the position of the hole 62 of the first extension cylinder 60 is retained in the interior wall of the first supporting cylinder 501 the elastic body 63 is still pressed by the interior wall of the first supporting cylinder 501 and the elastic force of the elastic body 63 cannot be released fig7 is a schematic diagram illustrating the first extension cylinder 60 pulled from the interior wall of the first supporting cylinder 501 according to fig6 as shown when the first extension cylinder 60 is pulled from the interior wall of the first supporting cylinder 501 and the hole 62 on the interior wall of the first extension cylinder 60 is not covered by the interior wall of the first supporting cylinder 501 the elastic body 63 then releases the elastic force to achieve the elastic displacement the elastic body 63 is then.