To issue an alarm with sound to a vehicle erroneously entering a road shoulder due to drowsy driving or inattentive driving when a disabled vehicle or a damaged vehicle is parked on the road shoulder of a freeway.

An alarm device is formed so that sound is generated at both ends of a hose. In the hose, a flow of air is blocked. When a tire A of a vehicle passes on the hose, the hose is compressed, air in the hose is highly compressed, a piston lock in a cylinder departs, and a piston is pushed out. Then, a detonator or gunpowder ignites with an impact, and sound is generated.