PROBLEM TO BE SOLVED: To prevent members for keeping a bag self-stand from becoming an obstacle for a loading, and make the load hardly left on the bottom four corners of the bag after a discharge.SOLUTION: Each side of four lateral faces, the right, left, front, and back faces, of a bag body made of sheet is connected to each other via a corner forming surface whose width is narrower than these lateral faces. Accordingly, the total shape is formed into a square cylindrical shape with its four corner parts cut off. Furthermore, poles in a band plate shape with rigidness are attached to the outside of these corner forming surfaces in the bag body height direction. Also, reinforcement bodies are attached at the outside center of the four lateral faces of the bag body. These poles and reinforcement bodies are formed by hollow plastic structure plates, and rod shaped core materials are inserted in the hollow parts.
