This gas-pressure actuator has: a launcher member; a gas generator that is disposed at a first axial end of the launcher member; a rocket member that is accommodated inside the launcher member; an end pad and a sealing gasket, each of which is disposed at a second axial end of the launcher member; and a gasket holder that holds the gasket. The rocket member has a first section at a position corresponding to the first axial end, and a second section having a smaller diameter than the first section and extending from the first section toward the second axial end. The end pad includes a positioning portion that positions the rocket member and restrains the displacement of the rocket member in a direction away from the first axial end. The gasket holder can be plastically deformed by being pressed by the first section when the rocket member projects from the launcher member.
