A diaphragm-type pressure sensor consisting of two optical fibers for SF₆ gas circuit breaker is described. The lights from two IR LEDs are mixed and put into a transmitting fiber. A receiving fiber receives the reflected light from the diaphragm and the reference light. The ratio of the reflected signal and the reference signal warrants precision of the measurement in even the presence of external fluctuations. The pressure measuring system has the measurement accuracy 3% of full scale over a pressure range of 0.1-3.0 MPa. The optical fiber pressure sensor is compared with a semiconductor pressure transducer by means of measuring the pressure in SF₆ gas circuit breaker.