Steel is circulating. Make changes itself to evolve constantly. The steel created from nature does not disappear, and have infinite eternity. It is a value and virtue of the physical properties of steel. Endless Triangle symbolizes eternity and the circulation of the iron. Here, the triangle is the basic unit for eternal circulation, and is the smallest unit for the shape and structure. Steel has the dual properties. It is tough, however, also sometimes flexible. It is depending on the used the way and processing of iron, which means the variety of physical properties. The rear plate having a male robustness to form a basic skeleton which consist the structure of the Endless Triangle. Luxteel, which has feminine delicacy, it makes up the epidermis of the structure upon the masculine plate. Endless triangle is clearly give eternal and diversity of properties of steel as structural aspect. Three-dimensional circulation structure reveals the spatial specificity. This is a beauty of the structure and as an essential power of architecture.