Provided are an airbag and an airbag device that are capable of reducing impact on an occupant at an out of position while providing restraining ability with respect to the occupant in a normally seated state. An airbag device includes an airbag 2 that is normally folded and accommodated in a seat 11 of a vehicle and that is inflated and deployed in an emergency, and an inflator 3 that supplies gas to the airbag 2. The airbag 2 includes a bag member 21 that is formed of a base cloth 2a, and a plurality of pleats 22 that are formed at the bag member 21. The pleats 22 have a crease portion 23 in a front-back direction of the vehicle to allow the gas to escape to the crease portion 23 upon loading from the front-back direction of the vehicle when the bag member 21 is inflated and deployed.