A head-protecting airbag device according to the present invention is mounted on vehicle by attaching an airbag module including an airbag and a roof rail garnish to vehicle. The garnish covers an interior side of the folded airbag. The airbag module includes a clip having a garnish side joint portion to be detachably engaged with the garnish, and a vehicle body side joint portion to be engaged with vehicle body in a state of holding a mounting portion of the airbag. In the clip, an engaging force of the garnish side joint portion with the garnish is predetermined weaker than an engaging force of the body side joint portion with the vehicle body, such that the garnish is detachable from the vehicle body while leaving the mounting portion of the airbag attached to the vehicle body. In the head-protecting airbag device of the present invention, maintenance of the roof rail garnish is facilitated.