An airbag provided with a pocket. An airbag (21) comprises a main bag body (31), an opening (32) formed in the main bag body (31), a small bag body (33) extending from the opening (32) to the inside of the main bag body, and a joining section (34) at which a part of the small bag body is joined to the main bag body. The joining section (34) is provided in the area which, when the airbag is expanded, extends from both the side surfaces of the airbag or from the top surface (72) of the airbag to the rear surface (73) which comes in contact with and holds the occupant.