A side curtain air bag unit includes a cover; an air bag housed in the cover; at least one mounting flap extending from the air bag and fastened to a vehicle body; a ramp holding the air bag and cover therein, mounted adjacent to an upper end of a B-pillar trim to guide deployment of the air bag such that the B-pillar trim does not interfere with the deployment; and a fastening member having a first end secured to the cover, and a second end which passes through the ramp and is secured to the body of the vehicle.