Providing an overturn preventing device which can easily be mounted between a top surface of an article and a ceiling and a method of mounting the overturn preventing device. The overturn preventing device includes a damper. The damper is mounted between a top surface of a piece of furniture (an article) and a ceiling. The damper includes a cylinder and a piston. A hydraulic fluid (operating liquid) and a compressed gas are enclosed in the cylinder. The piston is slidably housed in the cylinder. When the damper is to be mounted between the top surface of the furniture and the ceiling, the piston is housed in the compressed gas enclosed above the hydraulic fluid. The piston can be moved into the hydraulic fluid when the furniture is tilted and the damper is contracted by a predetermined length.