This paper is concerned with movements and stability of a man gazing at a moving picture in a darkroom. These experiments were studied to clarify the relation between visual information and postures. A worker may indirectly be exposed to vibration when the objects around him swing, for example by an earthquake. This is not only a problem for workers but also, when he operates a large plant, it is a problem for the system if he operates it erroneously. The bar picture was made with a computer and swings right and left in front of a subject in the first case, and, in the second case, the bar pictures start suddenly to the right side or to the left side and, after a constant time, they suddenly stop. As a result, one may stand more unstably under the following conditions: when the bars suddenly move or stop and when the equilibrium line of the bar vibration deviates right or left than when the line exits in the constant position. A man can stand more stably after a few trials than at the first or second trial. A man can swing his center of gravity when the bar swings in front of him. The picture is different from that which can make him unstable.