A curtain airbag capable of improving deployability of an airbag cushion without including a ramp component. The curtain airbag includes a main cushion, provided at an upper side of a pillar of a vehicle along a forward-and-rearward direction of the vehicle and configured to be deployed with inflation thereof, and a guide cushion, connected to a front area of an upper end portion of the main cushion and configured to extend toward a rear of the vehicle, the guide cushion pushing the main cushion toward an inside of the vehicle while being inflated together with the main cushion.