PURPOSE: To prevent accidents endangering lives at the time of a disaster at sea by fixing an air bag in a portable housing body with large outer diameter and connecting the air bag to a compressed air can.
CONSTITUTION: A lifesaving device 1 is exposed by pulling the end of a string in the upper portion of a rucksack. The exposed lifesaving device 1 has a detent plug 8, and air is sent from a compressed air can 9 to an air bag 2 by loosening the detent plug 8. Then the air bag 2 expands so that a man can enter it. Namely, the air bag 2 expands with the rucksack as a center so that the body having the rucksack enters the expanding air bag 2 automatically. When the air bag 2 expands perfectly, an entrance 3 and an entrance cover 6 in the upper portion are squeezed down properly. With this arrangement, shock against a water surface is prevented and a man's body is not soaked in water so that safety is enhanced.