PURPOSE: To prevent crawling of a colliding car from behind by narrowing a space between a bumper and a road surface, at the time of running on a normal road surface, and to prevent contact with the road surface by widening the space between the bumper and the road surface, at the time of running on a bad road, by providing an upper end part of the bumper turnably in a supporting point.

CONSTITUTION: When a changeover switch 7b of a control means 7 is closed in a side of a terminal (a) by a driver at the time of running on a normal road surface, a switching valve 7a is actuated to supply a pressure of oil to an oil chamber 6a of a fluid cylinder 6 by an oil hydraulic pump 8, and a bumper 4 is turned with a shaft 5 of an energy absorbing damper 3 serving as a supporting point, by moving a piston 6c in a direction of arrow mark A, and stopped in a position of vertically placing the bumper. Here by narrowing a space between a lower end part of the bumper 4 and the road surface, a colliding car from behind is prevented from getting in. On the other hand, when the changeover switch 7b is closed in a side of a terminal (b) by changing into bad road running, the piston 6c of the fluid cylinder 6 is moved in a direction of arrow mark B, and the bumper 4 is stopped in a position shown by a one-dot chain line to prevent the bumper lower end part from coming into contact with the road surface.