A roof airbag apparatus may include: a cushion configured to cover a roof when deployed; a pair of guides having a length in the deployment direction of the cushion, and configured to guide both sides of the cushion in the deployment direction; and a deployment resistance reducer having a connector connected to one end of each of the guides so as to apply an elastic force from a first location toward the rear, wherein the connector is moved to a second location in a front of the first location by frictional resistance which is applied to the guide when the cushion is deployed.