The head-protecting airbag apparatus of the present invention includes an airbag and a guide bracket. The guide bracket includes two guide walls and a joint wall, thereby has a generally U-shaped cross section, and accommodates the folded airbag between the two guide walls. The guide bracket is located above a pillar portion while being covered by an airbag cover, and serves to guide the inflating airbag toward vehicle's inner side and prevent the airbag from entering vehicle's outer side of the pillar garnish. The dimension of a clearance between the two guide walls is set such that: a gap arises between the housed airbag and at least one of the guide walls, thereby the airbag is allowed to inflate in the gap in the initial stage of airbag inflation; and that the deployment direction of the airbag is controlled by the guide walls, toward vehicle's inner side. In the head-protecting airbag apparatus of the present invention, the airbag housed in the upper periphery of windows smoothly protrudes inward of vehicle without providing any gas-leakage preventing means such as a reinforcing patch.