To provide a life jacket developing an expanding air chamber from inside of the life jacket to outside to completely protect whole of a body especially main parts of a body such as the cervical vertebra, the vertebra or the like by using a starting equipment that automatically and instantaneously acts by an actuate key, differing from a conventional protection on a fixed position.

This life jacket relieves a shock of a collision to a thrown out driver or passenger to a road surface, a structure on a road, a wall or the like which is understood as a characteristic phenomenon of a traffic accident of a motorcycle or the like, by installing plural air chambers which are stored in folded state, in the life jacket for the passenger of the motorcycle or the like and instantaneously expanding the air chambers by filling carbon dioxide gas supplied from a carbon dioxide gas cylinder connected to the starting equipment in two steps to the chambers in actuating time.