An exhaust path penetrating through a portion of a vehicle's body to exhaust air in a cabin of a vehicle with an air-flow activating means and a valve which opens only when the fresh-air activating means works, a fresh-air conducting path penetrating through a portion of said vehicle's body to conduct fresh-air into the cabin with an air-flow activating means and a valve which opens only when the air-flow activating means works, and an electric circuit which drives each of said air-flow activating means and each of said valves with electricity supplied from solar cells mounted on an external face of said vehicle's body to receive sunlight and generate electricity.