Abstract: The present invention utilizes the resilient force (i.e. the force to deform when pressure is added and to return to the original shape when the pressure is removed) of an elastic member or bias member. A large pressure if added in advance to the elastic member or bias member disposed in a preserver body to set the preserver body in a thin and flat state. In an emergency, the resilient force of the elastic member or bias member causes water or air to be sucked into the preserver body. The volume of the preserver body is expanded by the air sucked in due to the resilient force of the elastic member or bias member or by gas generated by a chemical reaction between the sucked-in water and a foaming agent. The increased volume causes the preserver body to float, thereby enabling a wearer to breathe.