An internal pressure explosion-proof system is provided that is capable of detecting high-pressure abnormality of an internal pressure explosion-proof mechanism, urging a check of gas/air apparatus by providing a means for notifying a user of abnormality, and decreasing excessive pressure of an internal pressure chamber. A high-pressure abnormality detector and a pressure regulating valve are provided in an air discharging portion for releasing the gas/air discharged from the internal pressure explosion-proof mechanism. The working pressure of the high-pressure abnormality detector is set to be lower than the working pressure of the pressure regulating valve. The high-pressure abnormality detector sends a signal when the pressure becomes higher than the set pressure to make the alarm give a warning and makes the open valves open to decrease the pressure of the internal pressure chamber of the internal pressure explosion-proof mechanism which became excessive.