A curtain airbag device capable of inflating and deploying without suffering a burst of a cushion part at an end of a cushion part protector near an inflator. The curtain airbag device includes a cushion part extending in a front to back direction of the vehicle, accommodated in a state rolled up from a lower end toward an upper end thereof, and inflating and deploying downward when gas is supplied thereto. The curtain airbag device includes an inflator for supplying gas to the cushion part from a predetermined position at the upper end of the cushion part, and an elongated protector 180 having an arc-like open curve cross section that is open downward and covering the cushion part, with an inner surface thereof making contact with the cushion part. The cross section of the protector being defined by the open curve, with an end point P of the open curve on a vehicle inner side smoothly going up at a first end near the inflator so that the open curve has an increasing distance between end points thereof.