To enable the absorption of larger impact energy than in the past in spite of the same size as a conventional bumper has.

A bumper 12 is mounted on a vehicle body 11 through a hydraulic cylinder 13. A throttle 19 formed with a check valve 20 in parallel and a communication shutdown switching valve 15 are provided in a space to an accumulator 16 as a pressure supply source connected to the hydraulic cylinder 13. A communication shutdown switching valve 15 is driven by a control unit 18 which is controlled by a collision detector 17 for calculating the signal of a vehicle-to-vehicle distance or vehicle speed and discriminating the presence of collision.