In order to provide a fluid device that makes it possible for operation command signals other than existing operation command signals to be received without a software modification having to be implemented in an already constructed system, in a fluid device that measures or controls physical quantities of a fluid, there are provided a command signal receiving unit that receives a predetermined plurality of types of operation command signals, and also command signal modes, which are values thereof or time series variations of the values thereof, and a command signal recognition unit that, when the command signal mode of a predetermined operation command signal received by the command signal receiving unit falls outside predetermined conditions that have been set in advance, recognizes the predetermined operation command signal that contains the command signal mode as being a different type of operation command signal.