A rotunda height adjusting device for a boarding bridge, wherein a fastened tunnel is connected to the boarding bridge, the device for enabling the rotunda to ascend and descend, the device comprising: an outer column fastenable to the rotunda; an inner column fastenable to a ground surface and arranged coaxially within the outer column; a vertical screw disposable at a lower end of the rotunda; a nut formed in a center portion of the inner column coaxially with the vertical screw, an internal diameter of the nut corresponding to an outer surface of the vertical screw, and the nut being engaged with the vertical screw and allowing the outer column to ascend and descend with respect to the inner column; characterized in that at least three pairs of convex rails and concave rails are provided by convex rails disposed on an outer side of the inner column engaged with concave rails disposed on an inner side of the outer column, wherein the convex rails and the concave rails are extending in a longitudinal direction of the inner column and outer column and a length of each of the convex rails and the concave rails corresponds to an ascending and descending distance of the outer column, wherein the pairs of convex rails and concave rails engaged with each other and the nut engaged with the screw distribute wind pressure and a lateral load on the rotunda, such that the outer column may ascend and descend in a safe manner. wherein a fastened tunnel is connected to the boarding bridge, the device for enabling the rotunda to ascend and descend, the device comprising: an outer column fastenable to the rotunda; an inner column fastenable to a ground surface and arranged coaxially within the outer column; a vertical screw disposable at a lower end of the rotunda; a nut formed in a center portion of the inner column coaxially with the vertical screw, an internal diameter of the nut corresponding to an outer surface of the vertical screw, and the nut being engaged with the vertical screw and allowing the outer column to ascend and descend with respect to the inner column; characterized in that at least three pairs of convex rails and concave rails are provided by convex rails disposed on an outer side of the inner column engaged with concave rails disposed on an inner side of the outer column, wherein the convex rails and the concave rails are extending in a longitudinal direction of the inner column and outer column and a length of each of the convex rails and the concave rails corresponds to an ascending and descending distance of the outer column, wherein the pairs of convex rails and concave rails engaged with each other and the nut engaged with the screw distribute wind pressure and a lateral load on the rotunda, such that the outer column may ascend and descend in a safe manner. an outer column fastenable to the rotunda; an inner column fastenable to a ground surface and arranged coaxially within the outer column; a vertical screw disposable at a lower end of the rotunda; a nut formed in a center portion of the inner column coaxially with the vertical screw, an internal diameter of the nut corresponding to an outer surface of the vertical screw, and the nut being engaged with the vertical screw and allowing the outer column to ascend and descend with respect to the inner column; characterized in that at least three pairs of convex rails and concave rails are provided by convex rails disposed on an outer side of the inner column engaged with concave rails disposed on an inner side of the outer column, wherein the convex rails and the concave rails are extending in a longitudinal direction of the inner column and outer column and a length of each of the convex rails and the concave rails corresponds to an ascending and descending distance of the outer column, wherein the pairs of convex rails and concave rails engaged with each other and the nut engaged with the screw distribute wind pressure and a lateral load on the rotunda, such that the outer column may ascend and descend in a safe manner.