Disclosed is an airbag apparatus capable of safely protecting a passenger by increasing the width of an airbag cushion in a leftward-rightward direction when the passenger comes into contact with the airbag cushion. The airbag apparatus includes: a first tether disposed inside the airbag cushion in a forward-backward direction, and a second tether disposed inside the airbag cushion in the leftward-rightward direction and connected to the first tether. When the passenger comes into contact with the airbag cushion upon deployment of the airbag cushion, the width of the airbag cushion in the leftward-rightward direction is increased.