The airbag of the head-protecting airbag apparatus includes a rear inflatable portion deployed at the interior side of the rear pillar. The rear inflatable portion includes an upper side portion extending rearward from a gas feed passage disposed at the upper periphery of the airbag, a main body disposed below the upper side portion and partitioned from the upper side portion by a partitioning portion, and a branched portion extending downward from the gas feed passage. The main body inflates with inflation gas fed from an inlet opening disposed at the lower end of the branched portion. At least a front lower area of the upper side portion is located below a parting line between a rear pillar garnish and an airbag cover at full inflation of the airbag. The upper side portion and the gas feed passage are folded and housed at exterior side of the folded-up main body and branched portion such that the main body is pushed out toward an interior of the vehicle getting over the upper end of the rear pillar garnish by the upper side portion and the gas feed passage.