An airbag device is provided in which the airbag is made by folding an airbag having a left airbag section and a right airbag section and wrapping the folded airbag by a shape-retaining sheet. In one form, an airbag includes a left airbag section and a right airbag section that are inflated on the left and right, respectively, in front of a passenger, and a base chamber that communicates base ends of the airbag sections with each other. The airbag is folded so as to have reduced vertical and longitudinal widths, and is wrapped by a shape-retaining sheet. An opening is provided in the shape-retaining sheet so as to face a lateral face of a folded body of the airbag on the passenger side.