Substrate processing apparatus and gas supply method

A gas supply method for a substrate processing apparatus including a processing container capable of accommodating a substrate, a flammable gas supply path configured to supply a flammable gas into the processing container, a covering structure provided outside the processing container and configured to include an inner covering body including a first space for accommodating a portion of the flammable gas supply path and an outer covering body including a second space for accommodating the inner covering body, an arrangement space adjusted to a negative pressure and in which the covering structure is arranged, a non-flammable gas supply configured to supply a non-flammable gas to at least the first space, an exhauster capable of exhausting a gas in the first space and a gas in the second space, and a pressure detector configured to detect information, respectively, relating to a pressure in the first space, a pressure in the second space, and a pressure in the arrangement space, the gas supply method comprising:

• during supply of the flammable gas, controlling at least one selected from the group of the non-flammable gas supply and the exhauster based on the information from the pressure detector so as to adjust the pressure in the first space to a positive pressure and adjust the pressure in the second space to a pressure lower than the pressure in the arrangement space or to a pressure higher than the pressure in the arrangement space but lower than the pressure in the first space.