PURPOSE: To safely protect a pedestrian or a bicycle from a collision by providing a deployable shock relaxing section at the front end section or the rear end section of a vehicle, and driving it when the calculated value of the degree of collision risk becomes a preset allowable value or above.

CONSTITUTION: A vehicle is provided with a front air bag 6 stored in the bumper of an automobile and deployed in front of the bumper when operated as a shock relaxing device, an obstacle detecting means 1 detecting an obstacle, a distance detecting means 2 detecting the distance to the obstacle, and a vehicle running state detecting means 3, and the output signals of them are inputted to a control device 4. The control device 4 estimatingly calculates the degree of collision risk with the obstacle in the advance direction of the vehicle based on the input values in a collision estimation section 41, deploys the front air bag 6 via a front air bag driving means 5 when the calculated degree of collision risk becomes a preset allowable value or above, and operates a collision warning device 7 and a seat belt driving means 8.