To prevent an air bag from being operated by mere inclination when the vehicle body does not fall down, that is, at the time of handling during a banking operation or the like. An air bag and a removal detecting part for detecting a rider removal from a vehicle body are incorporated in a rider jacket. An inclination sensor for detecting an inclination of the vehicle body of a motorcycle is provided. An angle acceleration calculating part for calculating the inclination angle acceleration of the vehicle body calculates the inclination angle acceleration based on a plurality of detected inclination angles. When the state of the vehicle body falls within the air bag operable range, an air bag deploying instruction is outputted. The air bag deploying instruction is supplied to the air bag when the rider removal from the vehicle body is not detected by the removal detecting part.