An airbag device 4 for pedestrian structured to drain water in a case to a cowl includes a case 8 for storing an airbag 5 in a folded state, an inflator 9 for inflating the airbag 5, and a lid 10 which closes an opening 3a of a hood 3, which allows passage of the airbag. Discharge passages 9 for draining water which has intruded into the case 8 to a cowl louver 2 are formed at both ends of the case 8 in a longitudinal direction.