Abstract: The present invention disclose a sack used in an ordinary sack and a hard type sack selectively according to the existence of a hard case. The ordinary sack can be sagged easily when goods is packed into the sack because a material of the sack is usually a soft synthetic fiber. Such softness gives a non-elegant and uncomfortable to carry the ordinary sack. In more, carrying fragile goods in such a sack can make someone to be nervous to prevent unpredicted external impact. Usage of the hard type sack has an advantage to keep a shape without sagging when goods are packed in, and to protect the goods from any external impact, because a backside case is made of a hard material. However, disassembling the backside case from the hard type sack is not easy because the backside case is jointed with a back supporter by bolts and nuts method. In more, bolts are always required to re-assemble the backside case into the hard type sack after disassembling.