A collision determination is made by using at least one of the output signals of a front G sensor disposed on a vehicle's fore-end and an analog G sensor disposed within the vehicle interior; a safety determination is made by using at least one of the output signals of the analog G sensor, the front G sensor, and a safing G sensor; and when both of the collision determining signal and the safing signal indicate the significance, an application specific IC and a transistor switch actuate a squib activating an air bag.