A roof airbag apparatus, may include an inflator, a housing mounted to an opening frame provided in a vehicle roof, the opening frame defining an opening therein to receive the housing, an airbag cushion contained in the housing, the airbag cushion being deployed downwards by gas supplied from the inflator to protect a passenger, an airbag door coupled to the housing by a hinge to support the airbag cushion, and angle limiting means for limiting a rotating angle to a predetermined angle when the airbag door is rotated to open.