Provided is an airbag configured so that, in the inflated state thereof, a recess is formed in a chest restraint area in the passenger facing surface of the airbag, and the portion of the airbag other than the recess has a large inflation thickness. A driver-side airbag 1 is formed by sewing a front panel 2 and a rear panel 3 together. The rear panel 3 is provided with a left tuck portion 12 which extends from the upper left to the lower left, and a right tuck portion 11 which extends from the upper right to the lower right. The tuck portions 11 and 12 increase the inflation thickness of the driver-side airbag 1. A recess 6 is formed in a passenger chest restraint area in the driver-side airbag 1 by a tether 20.