To provide a portable chair without legs (used in a tatami (rush mat) room) used in common as a bag by providing a box, which can be used as the chair without legs and opens at its top side, at the bottom of the bag.

The box 1 opening its top side is provided with a bottom surface as flat as possible and is made of the lightest material in weight such as a cane, which can support the weight of a human body. By making the box cushion material 5 freely attachable and detachable, it can be replaced with another one with the size and the height of a seat surface which is suited to the body shape of a user. For the bag 2, a proper sheet body such as leather is used and the bottom surface of the box 1 is fit with the bottom back surface 6 of the bag 2 to make the bag 2 at least the double structure of front and back surfaces 7 and 8. By providing a taking in/out port 9 for taking in/out to/from the box 1 is provided at the both face part, the box 1 can be taken in/out to/from both surfaces and the box 1 can be replaced with another of user's favorite height and width. The bag 2 housing the box 1 provided with the material 5 is used for sitting as a chair by facing its bottom face upward and used as the bag 2 by putting things in it as the opening part of the box 1 faces upward.