A pressure control system is disclosed. The control system in one embodiment includes a main body comprising a pilot chamber wherein an intake port and a discharge port are formed, and a spool comprising an upper slide and a lower slide. The spool in this embodiment is attached by a spring to the upper part of the main body. The exhaust apparatus pressure control system includes an absolute pressure sensor for detecting the pressure in the intake port and a differential pressure sensor for detecting the difference between the pressure in the intake port and atmospheric pressure; a control valve for supplying a pressure regulating gas to the pilot chamber; and a control circuit for sending switching signals to the absolute pressure sensor and the differential pressure sensor, and driving the control valve based on the output from the absolute pressure sensor or differential pressure sensor.