To provide a liquid shutoff valve device provided with an open/close valve excellent in reliability in which the valve closes without rapidly increasing a pressure inside a container at the time of rising of a liquid level, and surely opens at the time of lowering of the liquid level.

A mushroom valve 22 is provided which is seated on an opening 10g prior to opening of a float valve 15 upon reception of an exhaust gas pressure and restricts a flow rate of the exhaust gas by an air vent 22d. The float valve 15 comprises: a main packing 20 provided to be movable with respect to a float 11, and urged at increase of the float 11 to seal a space between an outer peripheral edge of the mushroom valve 22 and the opening 10g; and a subsidiary packing 21 which is provided to the float 11, seals the air vent 22d by ascending of the float 11, and makes, by descending of the float 11, the air vent 22d open prior to the opening of the main packing 20.