A vertical pneumatic fender comprises a fender body having bowl-shaped hemispherical portions joined to both ends in the axial direction of a cylindrical body portion, and a weight that is connected to the bottom of the fender body. The vertical pneumatic fender accommodates ballast water in an interior space of the fender body, and is provided with a backup chain. One end of the backup chain is connected to the fender body in a position that is offset with respect to the axial line of the fender body, and the other end is connected to the weight. The fender body and the weight are connected with the backup chain in a sack state. The slope of an axial orthogonal reference line and an axial parallel reference line are detected by way of a reference line detector.