A check valve includes a valve case, a positive pressure valve, a spring, and a negative pressure valve. The positive pressure valve is slidably disposed in a valve chamber of the valve case. The spring urges the positive pressure valve to abut on a positive pressure valve seat of the valve case. The negative pressure valve is on the positive pressure valve to abut on a negative pressure valve seat of the positive pressure valve. The negative pressure valve closes a communicating passage in the positive pressure valve in a normal state, and opens it when a pressure in the fuel tank falls to a predetermined value or less.