A valve device capable of automatically and surely performing such an opening and closing control that, when gas is forced to be passed after liquid is passed, a pipeline is cut out, providing excellent sealability at the time of valve closing and stable operation, and making difficult for a chattering, hunching, or water hammer to occur immediately before valve closing or the moment the valve starts to open and automatically exhausting the residual gas inside the pipeline at the time of START of or during the feeding of the liquid and a pipeline system capable of being controlled automatically by the use of the valve device the valve device, characterized by comprising a valve having a valve disc interlocked with a float opening when the float rises and closing when the float lowers and an auxiliary valve closed when an acting force of a specified value or higher caused by a pressure inside a flow path is added thereto and opened when the added force is removed, the pipeline system and characterized in that the valve device is installed at the inlet of a terminal device in the pipeline system allowing the residual liquid inside the pipeline to be drained by the force-feeding of the gas into the pipeline after the liquid is fed to at least one terminal device through the pipeline.
