A roof airbag apparatus including a rear cushion unit deployed from a rear part toward a front part of a roof when gas is supplied, and covering a rear region of the roof; a front cushion unit coupled to a front end of the rear cushion unit to communicate therewith, deployed forward when the rear cushion unit is deployed, and covering a front region of the roof; a pair of guide bars guiding left and right ends of the rear cushion unit and the front cushion unit at left and right sides of the roof; and a pair of connection members coupled to front ends of the guide bars in a state in which the pair of connection members are fixed to the front part of the roof, and decoupled from the guide bars and deploying the front cushion unit downward when a front collision sensing signal is transferred.