Provided is an airbag having a function for controlling bag-section expansion while also retaining air-tightness, by reducing the concentration of stress applied to restriction threads during deployment. Provided is a bag body having, in the interior, restriction threads for restricting expansion, wherein the restriction threads comprise: first yarn extending in the interior of the bag body from a non-expanding section to a different non-expanding section; second yarn which forms a base fabric of one side of an expanding section of the bag body and which is separated from the one side and is caught on the first yarn, or is woven with the first yarn to constitute a structure, again returning to the base fabric of the one side; and third yarn which forms a base fabric of the other side of the expanding section of the bag body and which is separated from the other side and is caught on the first yarn, or is woven with the first yarn to constitute a structure, again returning to the base fabric of the other side.