To instantaneously determine a collision against a collision preventive wall for an expressway of a car and a damaged status by the collision by a road administration division at a remote place.

Collision sensors 46 are installed to the expressway collision preventive wall, and a transmitter 40 is connected to the collision sensors 46. When the collision sensors 46 detect the collision, a radio frequency signal is transmitted to the remote place. The radio frequency signal contains a trouble message automatically transferred to users 64 responsible to the maintenance of the collision preventive wall. A camera 42 catches the image of the collision preventive wall immediately after the collision in a storage device 43 in response to outputs from the collision sensors 46.