To provide a bag with a high fashionableness, in which two entirely different styles can be formed from one bag, and in which capacity can be easily increased/decreased accordingly, eliminating rusticity of having useless extra capacity for expansion.

The bag is characterized in that, to the outer periphery of two pieces of material of a prescribed shape formed symmetrically with respect to the center axis, fasteners with their ends connectible to each other are attached, that an inserting origin is provided in each of the opposing two points on the center axis in one of the two pieces of material, that an inserting origin and a slider are each installed at one point on the center axis in the other piece of material, and that a belt is provided. By connecting with the inserting position varied of the two pieces of material, a two-way bag having different styles and different capacities is available.