The present invention relates to an expansion-type bulk bag appropriate to load various seafood such as oysters and mussels, from a ship to a dock or to carry the seafood to a processing plant. The bulk bag includes a bottom surface (10), a plurality of side surfaces (20a-20d) having one sides connected with an outer circumference of the bottom surface (10), a plurality of extending surfaces (30a-30d) which have opposite sides connected with adjacent side surfaces, form the same plane as a plane formed by the bottom surface 10 in the surface that the side surfaces (20a-20d) are spread, and are folded while being wrinkled inward of the side surfaces (20a-20d) adjacent to each other in the state that the side surfaces (20a, 20d) are folded and are in an upright state, coupling members (40a, 40b) which are installed on the adjacent side surfaces (20a, 20d) connected with the extending surfaces (30a-30d), a plurality of rings (50) which are provided along an outer circumference of the extending surfaces (30a-30d), and ropes (60a, 60b) which have opposite ends fixed to facing side-surfaces (20a, 20b) of the side-surfaces (20a-20b) inserted into the rings (5) provided along the outer circumference of the expending surfaces (30a-30d) and extend along an outer circumference of different side surfaces (20c, 20d) adjacent to the face side-surfaces (20a, 20b).
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