A curtain air bag system includes a main deployment portion for an occupant seated in a front seat, that is housed folded up in an upper edge portion of an opening in a vehicle body, and inflates by receiving a supply of gas when the vehicle is in a side collision and when the vehicle rolls over, and deploys in a curtain shape downward with respect to the vehicle; an auxiliary deployment portion that inflates by receiving a supply of gas via a gas passage that is communicated with a portion of the auxiliary deployment portion in a vertical direction of the vehicle, and that deploys such that a lower end side, when viewed from a side, overlaps with a side door forward of the main deployment portion; and a connecting portion that connects a portion on an upper end side of the auxiliary deployment portion to a front pillar.