An airbag device for the body instantaneously activates an airbag without malfunctions.When an absolute value of an angular velocity detected by an angular velocity sensor exceeds a predetermined angular velocity value, angular velocity values are integrated from a most recent detected value to an oldest value within a predetermined time period, and if an absolute value of a resultant value of integral exceeds a predetermined value and an acceleration detected by an acceleration sensor is smaller than a predetermined acceleration, the airbag is inflated. Based on the value of the integral of the angular velocities, a case in which an angular velocity gradually increases is distinguished from a case in which an angular velocity momentarily increases, so the airbag device effectively prevents malfunctions caused by an action other than falling over. Additionally, because it is unnecessary to intentionally delay determination to prevent malfunctions, the airbag can instantaneously be inflated.