To simplify the work to improve the efficiency and improve the accuracy in construction and safety management by allowing a measuring instrument to vertically stand by itself on a circular tube, and determining a central position and a height only by adjusting one point.

Rubber plates 4 on both sides of a bottom of a cylindrical horizontal plate 1, arms with rubber plates 2 on the left and right sides of the cylindrical horizontal plate 1, a level vial 5 on an upper central part, and a scale 3 in the vertical direction are integrally formed. Whereby the cylindrical horizontal plate 1 with the level vial can stand by itself on a central position of the circular tube without dropped or moved, by means of the antislipping rubber plates 4 on the bottom and the left and right arms 2 with rubber plates 2, a height and centripetal force are simultaneously displayed by the integrated vertical scale 3, and the adjustment can be executed by anyone while observing the same.