Abstract: An air bag system is provided with an air bag body, an inflator unit, and a sensor unit. The sensor unit is provided with a first sensor which detects an impact of a vehicle, a second sensor which detects a rolling-over of the vehicle, and a controller. When an impact of the vehicle is detected by the first sensor, the first inflator is actuated so that gas is supplied to the air bag body. Thereby, an internal pressure of the air bag body reaches a first pressure. When a rolling-over of the vehicle is detected by the second sensor, both the first and second inflators are actuated. Thereby, the internal pressure of the air bag body reaches a second pressure higher than the first pressure.