To provide a structure easy in removal in the maintenance and repairing of an air bag device at a clip and to enhance the mounting strength of the clip relative to a roof side rail upon the inflated deployment of the air bag.

This curtain air bag device is provided with an interior material 1 mounted to the cabin-side face of the roof side rail 2 by an engagement means 4 provided with the clip 5; the air bag 7 stored in an air bag storage chamber 3 formed on the interior material 1 in a folded state; and a mounting piece 7a extending from the air bag 7 and engaged with the engagement means 4. A first engagement part 5g for engaging the interior material 1 with the roof side rail 2 and a second engagement part 5e for engaging the mounting piece 7a are formed on the clip 5. In the deployment of the air bag, a tensile force generated on the mounting piece 7a is applied to the second engagement part 5e and a mounting/retaining force relative to the roof side rail 2 at the first engagement part 5g is increased.