PURPOSE: To simplify the structure of a stopper device as well as eliminate the failure of the engagement of its coupling portion by a method in which a stopper body coupling with the toothed portion of leg rack by the rising and turning actions of threaded shafts is provided and the upper and lower sides of the stopper body are adjusted by nuts screwed with the threaded shafts.

CONSTITUTION: When fixing a leg B and a working platform A together, the position of a stopper body 8 is adjusted to the place where a leg rack D is moved and stopped by means of nuts 9a, 9b, 10a, and 10b, coupled with the toothed portion of the leg rack D by rotationally erecting threaded shafts 4 and 5 in the direction of the leg rack D, and then fixed by the insertion of a wedge 11. Then, when moving the leg B and the working platform A relatively, the wedge 11 is removed, the threaded shafts 4 and 5 are fallen down toward a wedge receiver 1 side, and the stopper body 8 is separated from the leg rack D.