A pedestrian airbag system is mounted to a rear portion of a vehicle's sheet metal hood panel. An airbag is inflated to cover an area from the rear portion of the hood panel to a front side of a front pillar by being supplied with inflation gas; a case accommodates the airbag, and an airbag cover formed of synthetic resin covers the upper side of the folded airbag to allow projection of the airbag when inflated. The air bag cover is disposed at the hood panel's rear portion so the airbag cover's upper surface is continuous with the upper surface of the hood panel, elongated in the width direction of the hood panel, and mounted to the hood panel to be capable of moving in the width direction of the hood panel. Deterioration of the airbag cover's appearance due to thermal expansion can be prevented.