There is provided a substrate processing apparatus that includes a process chamber in which at least one substrate is processed; a gas supplier configured to supply a gas; and a buffer structure. The buffer structure includes at least two plasma generation regions in which gas is converted into plasma by a pair of electrodes connected to a high-frequency power supply and an electrode to be grounded, a first gas supply port that supplies a gas generated in a first plasma generation region among the at least two plasma generation regions, and a second gas supply port that supplies a gas generated in a second plasma generation region among the at least two plasma generation regions.