PURPOSE: To obtain a differential pressure detector which can judge the abnormality within a detector by providincj a pressure buffer member between a reference pressure introduction port and a reference pressure chamber for relaxing the I/O of a reference fluid and reducing the amount of I/O of reference fluid as compared with the amount of leakage between a reference pressure chamber and a pressure introduction port to be measured.

CONSTITUTION: A pressure buffer member 17 consisting of a porous film 17a is provided between a reference pressure introduction port 11a and a reference pressure chamber 12 to relax I/O of atmospheric pressure. A differential pressure detector 10 introduces atmospheric pressure from the introduction port 11a and a pressure to be measured from a port 11b for introducing pressure to be measured, detects the differential pressure between the atmospheric pressure retained at the reference pressure chamber 12 and a pressure to be measured using a differential pressure detection element 13, and then calculates the pressure to be measured using an external CPU and then displays it. In this case, when the sealing between a reference pressure and a pressure to be measured is improper and a positive pressure (a pressure to be measured > a reference pressure) is applied, a fluid to be measured flowing to the reference chamber 12 is prevented by the film 17a, thus preventing a differential pressure from being generated. Also, when a negative pressure is applied, the flow-in of the atmospheric pressure can be prevented and no differential pressure is generated. Therefore, if an output value which is equivalent to that when there is no differential pressure, a detector is judged to be faulty.