VEHICLE SAFETY DEVICE

PROBLEM TO BE SOLVED: To quickly and surely expand an air bag by providing a first end part extending radially inward from a center wall part and a second end part which has a radial part extending radially inward from a center inner wall part in a direction directing to a shaft, on a diffuser having the center wall part. SOLUTION: A first end part 110 of a diffuser 100 has a truncated cone wall part 132 which is axially away from a cylindrical side wall 122 and extends inward and prevents the radial moving of a first end part 70 of an inflator 40 by engaging to the first end part 70. A second end part 120 of the diffuser 100 is constituted of a curl part 140 extending radially inward from the cylindrical side wall 122 and prevents the axial moving of the inflator 40 in a second shaft direction and prevents the axial moving of the second end part 80. When a vehicle receives a horizontal impact, ignition agent 50 ignites, expanded fluid 46 is heated and flows from the inflator 40 into an air bag via a diffuser chamber 128 to expand the air bag.