PURPOSE: To surely protect an occupant by appropriately performing inflation deformation of a bag main body.

CONSTITUTION: An air bag is provided with a bag main body 1 of a bag shape having a gas inlet 13 continuing to an inflater 3 and a flow shift fabric 2 is provided in the inside of the bag main body 1 in such a state as covering the gas inlet 13. Gas flow ports 21 with prescribed diameter are formed in the outer circumferencial part except right above the gas inlet 13 and gas jet flow flowing from the gas inlet 13 is shifted in the side direction by the flow shift fabric 2 so as to be supplied in the bag main body 1 through the gas flow ports 21.