A curtain air bag system includes a curtain air bag that is housed folded up in an upper edge portion of a door opening, and that includes a first deployment portion that deploys when a vehicle is collided with in a side collision as well as when the vehicle rolls over, and a second deployment portion that deploys at least when the vehicle rolls over, by receiving a supply of gas. The first deployment portion deploys in a cylindrical shape extending in a vehicle longitudinal direction, above a belt line such that a rear end side of the first deployment portion overlaps with a center pillar when viewed from a side of the vehicle, and the second deployment portion deploys such that a lower end extends below the belt line, in a position not overlapping with the first deployment portion when viewed from the side.