To prevent falling of side plate parts and to upright them while maintaining simple and quick assembly, in a box body which maintains the shape of the box body by a fixing string wound around the side plate parts when assembling.SOLUTION: A pair of opposing side plate parts (25, 25) out of side plate parts includes wings (50) extending from both side ends respectively, and each wing (50) includes a wing penetration hole (51) through which a fixing string (S) passes. The fixing string (S) is provided so as to pass by going around each side plate part penetration hole and each wing penetration hole so that side plate parts (20, 23, 25, 25) stand upright. Each wing (50) is folded inwardly along adjacent side plate part (20) and is overlapped with the adjacent side plate part (20), and the wing penetration hole (51) has an overlapped portion (D) through...
