AIR BAG

PROBLEM TO BE SOLVED: To provide an air bag which can be developed smoothly and surely to a preset and predetermined developing direction and has good productivity.SOLUTION: The air bag includes a baggy air bag body part 31 which is expanded by the expandable gas introduced from a gas introduction part and is developed downward along the predetermined surface 24 of a vehicle compartment. The air bag body part 31 has an developing base part 38 which is developed by the expandable gas form the gas introduction part. The air bag body part 31 has an developing tip part 39 which is connected to the developing base part 38 and is developed by the expandable gas after the developing base part 38 is developed. The air bag body part 31 is changed over from such a first state that the air bag body part is folded so that the width size thereof becomes longer than the vertical size thereof to such a second state that a part thereof is pushed upward from below and curved, and the air bag body part is disposed on the predetermined surface 24 while being kept in the second state.