A valve device includes a valve body that defines flow paths, a diaphragm provided so as to be capable of opening and closing the flow paths, an operation member provided so as to be capable of moving in opening and closing directions that open and close the flow paths by operating the diaphragm, a main actuator that applies a driving force corresponding to an operating pressure applied in the opening direction or the closing direction of the opening and closing directions with respect to the operation member, a switching mechanism capable of selectively switching a position of the operation member that regulates a degree of opening of the flow paths between a first open position and a second open position in accordance with a magnitude of the operating pressure, and regulating mechanisms capable of independently regulating the first open position and the second open position.