An airbag includes a chamber that expands due to gas being introduced at a time of deployment and a non-expanding area that does not expand at the time of deployment, in which the airbag deploys by gas being introduced into the chamber. A first portion inside the chamber that is located around the non-expanding area includes a tip end portion that is closed, and at the time of deployment, the tip end portion applies a load to and becomes in contact with a second portion of the chamber that is located around the non-expanding area and that faces the tip end portion.