PURPOSE: To prevent cover fragments from being scattered to the occupant side and prevent a deployed air bag cover from interfering with the occupant by breaking and deploying the air bag cover in two side directions different from the inflation and deployment direction of a bag main body.

CONSTITUTION: An air bag device is provided with a thin breakable section 16 disrupting an air bag 4 into two from the vertex section 4a of a box-like air bag cover 4 made of a resin material and covering an inflator 2 and a bag main body 3 to the periphery side 4b and a cover deploying means 17 guiding the gas pressure generated by the inflator 2 astride the periphery side of the inflator 2 and the periphery side 4b of the air bag cover 4 and applying the tearing load to the air bag cover 4 in the direction to disrupt it across the breakable section 16.