A curtain airbag device (10, 110) provided with an airbag (12, 152) that is disposed along a roof side rail of a vehicle interior, and that can deploy so as to cover a window portion on a side face, the curtain airbag device (10, 110) comprising: a cover that covers the airbag (12, 252), at least, in a part of the folded or rolled airbag in the longitudinal direction, wherein the cover is formed of a pliable fabric material having a plurality of polymer fibers, and is configured to maintain the shape of the airbag (12, 252) through mutual fusion of at least a part of the polymer fibers; and a high stiffness portion (236, 265, 291) harder than other portions and formed during the fusion of the cover is provided, in the cover, the high stiffness portion (236, 265, 291) extending in the longitudinal direction of the cover, a base fabric extension portion (224, 252a, 282, 292, 295) that extends from the airbag (12, 252) is provided on an upper edge of the airbag (12, 252); attaching means for attaching the airbag (12, 252) to the vehicle is connected to the base fabric extension portion (224, 252a, 282, 292, 295); and at least a part of the base fabric extension portion (224, 252a, 282, 292, 295) is covered by the cover, wherein the base fabric extension portion (224, 252a, 282, 292, 295) has an outer portion that extends outside the cover member (18, 220, 230, 250, 266, 280, 290, 294) through a slit (222, 232a, 232b) provided in the cover, characterized in that the outer portion of the base fabric extension portion (224, 252a, 282, 292, 295) is folded back in a body part direction of the airbag (12, 252), and is connected by sewing, along with the cover and other portions of the base fabric extension portion (224, 252a, 282, 292, 295) inside the cover. a cover that covers the airbag (12, 252), at least, in a part of the folded or rolled airbag in the longitudinal direction, wherein the cover is formed of a pliable fabric material having a plurality of polymer fibers, and is configured to maintain the shape of the airbag (12, 252) through mutual fusion of at least a part of the polymer fibers; and a high stiffness portion (236, 265, 291) harder than other portions and formed during the fusion of the cover is provided, in the cover, the high stiffness portion (236, 265, 291) extending in the longitudinal direction of the cover, a base fabric extension portion (224, 252a, 282, 292, 295) that extends from the airbag (12, 252) is provided on an upper edge of the airbag (12, 252); attaching means for attaching the airbag (12, 252) to the vehicle is connected to the base fabric extension portion (224, 252a, 282, 292, 295); and at least a part of the base fabric extension portion (224, 252a, 282, 292, 295) is covered by the cover, wherein the base fabric extension portion (224, 252a, 282, 292, 295) has an outer portion that extends outside the cover member (18, 220, 230, 250, 266, 280, 290, 294) through a slit (222, 232a, 232b) provided in the cover, characterized in that the outer portion of the base fabric extension portion (224, 252a, 282, 292, 295) is folded back in a body part direction of the airbag (12, 252), and is connected by sewing, along with the cover and other portions of the base fabric extension portion (224, 252a, 282, 292, 295) inside the cover.