A substrate processing apparatus includes a stage provided in a chamber, a shower head in which a plurality of slits are formed and which is opposed to the stage, a first gas supply part which supplies a first gas to a space between the stage and the shower head via the plurality of slits, and a second gas supply part which supplies a second gas which is not a noble gas to a region below the stage, wherein the second gas is the same gas as one of a plurality of kinds of gases constituting the first gas in a case where the first gas is a mixture gas constituted of the plurality of kinds of gases, and the second gas is the same gas as the first gas in a case where the first gas is a single kind of gas.