Oxygen cylinder regulator with flowmeter & humidifer is fitted with safety valve. Once the flow rate has been set, the regulator will automatically maintain a constant flow rate irrespective of changing volume of cylinder contents. If the oxygen line distal to the regulator should be blocked, the regulator automatically prevents the build up of an excessive pressure in the apparatus and tubing between the outlet of the regulator and the obstruction. A pressure gauge indicates the cylinder contents. The flowmeter with humidifier is used in reducing gas pressure and adjusting gas volume, which rescue patient and treat as oxygen therapy by the hospital.