An airbag for rear-end collision of a vehicle is accommodated in the interior of the vehicle while being folded in a state extending along a lateral direction of the vehicle. When supplied with gas, the airbag is inflated and deployed in a part of the passenger compartment rearward of the rearmost seat. The airbag has a supply port and a distribute section. The supply port permits gas to be supplied to the interior of the airbag. The distribution section is connected to the supply port. The distribution section distributes gas that has passed through the supply port end sections of the airbag in the lateral direction of the vehicle.