Provided are an airbag in which an airbag main body section can be effectively unfolded inside a vehicle compartment. The airbag includes an airbag main body section formed in a bag shape, and a gas introduction section that communicates with the airbag main body section, and to which gas is supplied. The airbag main body section in a folded state has a first roll fold section formed by folding a tip side in an unfolding direction, and a second roll fold section formed by folding at least a portion on a base end side in the unfolding direction from the first roll fold section, and having a roll center at a position different from a roll center of the first roll fold section.