A valve-closing pressure chamber and a valve-opening pressure chamber are arranged on both sides of a main diaphragm inside an outlet shutoff valve. An upper supply/discharge tube and a lower supply/discharge tube are connected to a housing forming the outlet shutoff valve. The upper and lower supply/discharge tube supply and discharge air to and from the valve-closing pressure chamber and the valve-opening pressure chamber, respectively. An opening end, which is on the pressure chamber side, of each supply/discharge tube is obliquely cut relative to the direction of axis of the supply/discharge tube, which increases the opening area of the opening end. This prevents water present in the pressure chamber from adhering to the opening end of each supply/discharge tube and prevents the adhered water from freezing. As a result, operation performance of the outlet shutoff valve is enhanced.
