A main body for a carrying box includes first and second side walls, and a pair of first connection walls and a pair of second connection walls that are pivotally hinged to opposite ends of the first and second side walls and are pivotally hinged to each other. The main body further includes a latch assembly having a bracket and a latch disposed at the first and second side walls, respectively. When the first and second connection walls pivot, a distance between the first and second side walls is reduced and a volume of the main body is reduced. The bracket is automatically fastened to the latch as the bracket and the latch are pressed toward each other.