To provide a curtain air bag apparatus which has a few components, and a simply structured tension applying mechanism.

The curtain air bag apparatus 20 is provided in the range from an A-pillar 10 to a C-pillar 12 via a roof side-rail 11 of an automobile. In case of side collision and rolling-over, a curtain air bag 21 can be developed by the gas supplied from an inflater 22 so as to cover a B-pillar 14, a front door 15, and window openings 15a, 16a of a rear door 16 in the range from the A-pillar 10 to the C-pillar 12. In order to apply a tension to the lower side of the developed curtain air bag 21, a wire 30 is elongatedly arranged as a wire member through an opening 21c in the almost vertical direction. In the state that the curtain air bag 21 has been completely developed, the wire 30 is tightly stretched within the range between the opening 21c and a fixing member 25, and within the range between the opening 21c and an anchor 31 respectively. As a result, the tension is applied to the lower side of the curtain air bag 21.