To provide a system for controlling the flow of air, passing through a processing room of a semi-conductor industry, a medical laboratory or a biological laboratory, in which a pressure is kept at a value lower than an atmospheric pressure to prevent the releasing of a microbe to the outside of the room, by controlling a local vacuum in the area such as a processing device or an exhausting hood.

The system for measuring the pressure of gas in the area comprises a buffer gas supplying means, a flow passage, through which the buffer gas flows from the supplying means to the processing area, and a pressure transforming device 54, provided so as to be neighbored to the flow passage to measure the pressure of the flow passage.