A bag body of an airbag includes a recessed area that is sunken forward and extends vertically generally at the center in a left and right direction of the passenger side wall. The airbag internally includes a vertical tether that pulls the front end of the recessed area forward at airbag deployment. The airbag further includes two horizontal tethers; an upper horizontal tether and a lower horizontal tether, which connect the left side wall and right side wall of the bag body, respectively, and are deployable generally in a left and right direction in order to limit the clearance between the left side wall and right side wall. The upper horizontal tether is located in an area above the vertical tether and the lower horizontal tether is located in an area below the vertical tether.