Abstract: The present invention relates to a gas regulator which can limit the pressure of gas flowing into the gas regulator, thus allowing the gas regulator to be operated safely. When gas having pressure higher than a preset reference pressure flows into the gas regulator, an auxiliary cylinder unit is automatically closed by a preset reference pressure, thus preventing damage to the gas regulator caused by the carelessness of a user. The gas regulator uses a piston instead of a conventional diaphragm, thus being semi-permanently usable and almost completely preventing leakage of gas from the gas regulator. The springs of the auxiliary cylinder chamber and the main cylinder chamber have different elasticities, thus letting different forces be applied to the auxiliary piston and the main piston in response to the inflow of high pressure gas, so that the auxiliary piston and the main piston may be operated together or independently.