PURPOSE: To prevent a gas with the pressure higher than a set pressure from feeding to the downstream side resulting from a high pressure gas leaked to the inside owing to a defect of a sealing part and the like, in the regulator of a half closed type respiration device.

CONSTITUTION: In the regulator 83 of a half closed type respiration device, a release valve 860 is installed to its housing side wall. When the valve 860 is opened, a pressure setting chamber 837 inside the regulator 83 communicates with an outer side opening chamber 865, and the gas in the pressure setting chamber 837 is discharged to the outer side. Consequently, even though a high pressure gas is leaked and invades into the pressure setting chamber 837, it is exhausted to the outer side by the release valve 860, and the pressure of the regulator 83 is maintained constant constantly. Consequently, a gas with the pressure higher than the set pressure is never fed to the downstream side.