PURPOSE: To provide the portable bag by which going-out can be executed in a lightly dressed state, and also, which can cope with sudden shopping by varying its form.

CONSTITUTION: A bag main body 12 is formed by joining the outside periphery of the bag with a slide zipper, and forming its joined part to a separable state. In the inside of this bag main body 11, a bag forming sheet 20 which can form a bag by drawing out a string provided in its periphery is provided. This bag forming sheet 20 has a square shape and becomes a portable bag 10 by providing it so that the string is exposed to the outside in its corner part, and also, by attaching the divided bag main bodies 12 to the opposed corner parts of this bag forming sheet 20, respectively.