The curtain airbag includes: a curtain bag section configured with cloth panels joined in a bag shape, housed prior to use in a folded state in a vehicle roof side edge section and deploying and inflating downwards when injected with deployment gas; a collision detector for detecting a collision and/or signs of an imminent collision of the vehicle; a gas generator for supplying the deployment gas to the curtain bag section in response to a detection result of the collision detector; and a guide member configured with a cloth panel, rolled up from the bottom of the curtain bag section that has been folded prior to use, via the vehicle width direction inside towards the top of the curtain bag section, the guide member being disposed at a position overlapping with the vehicle front-rear direction position of an interior member provided inside the vehicle compartment.