A curtain airbag mitigating possible occupant ejection from a vehicle. The curtain airbag includes a serial main chamber that is capable of being inflated and deployed along a vehicle cabin side face; a delay chamber that is positioned at a front end section of the serial main chamber and that is inflated and deployed so as to overlap an A1 impact point below an A-pillar of the vehicle; and an ace tab that fixes the upper edge of the delay chamber to the A-pillar. The ace tab is provided at a position overlapping a straight line LS that is provided on the shortest way from the A1 impact point to the A-pillar, as viewed from inside the vehicle cabin.