The head-protecting airbag apparatus is mounted on a vehicle whose third-row seat is so put away as to stand proximate to the inner side of a window. The airbag has three shielding portions, and includes a dividing recess between the third shielding portion and second shielding portion. In the event that the third shielding portion engages the folded seat during the course of airbag deployment, the dividing recess separates the lower edge of a region between the second shielding portion and the third shielding portion, so that the second shielding portion is not hindered from smooth development.