Abstract: Providing an overturn preventing device which can easily determine whether or not the damper is properly mounted. The overturn preventing device is mounted between a top surface of a piece of furniture (an article) and a ceiling. The overturn preventing device includes a damper. The damper includes a cylinder, a rod, a piston and a rod cover. The cylinder encloses a hydraulic fluid (operating liquid) and a gas. The rod is reciprocably inserted into the cylinder. The piston is slidably housed in the cylinder. A proximal end of the rod is coupled to the piston. The rod cover has one of two ends coupled to a distal end side of the rod thereby to be reciprocable together with the rod. The opening side end of the rod cover is located on a side of the bottom side end of the cylinder relative to the opening side end of the cylinder when the piston is immersed in the operating liquid.