An active safety device for a motor vehicle comprises: obstacle detection device for detecting an obstacle; vehicle path prediction device for predicting a future path of the vehicle; collision possibility calculation device for calculating the possibility of a collision between the vehicle and the obstacle; and collision responding device for informing a driver of the presence of the obstacle or controlling the vehicle so as not to approach the obstacle according to the possibility of the collision between the vehicle and the obstacle, wherein the device further comprises: obstacle storage device for storing a position of the obstacle; and position estimation device for estimating a relative position between the vehicle and the obstacle from the position of the obstacle stored by the obstacle storage device, a vehicle speed of the vehicle, a yaw angular velocity of the vehicle, and a sideslip angle of the vehicle.