A substrate processing apparatus of the present invention comprises: a processing chamber for storing and processing substrates stacked in multiple stages in horizontal posture; a processing gas supply unit for supplying two or more types of the processing gases to the inside of the processing chamber; an inactive gas supply unit for supplying an inactive gas to the inside of the processing chamber; and an exhaust unit for exhausting an atmosphere of the inside of the processing chamber, wherein the processing gas supply unit has at least two processing gas supply nozzles which extend running along an inner wall of the processing chamber in the stacking direction of the substrates and supply the processing gas to the inside of the processing chamber, and the inactive gas supply unit has a pair of inactive gas supply nozzles which are provided so as to extend running along the inner wall of the processing chamber in the stacking direction of the substrates and so as to sandwich at least one processing gas supply nozzle of the at least two processing gas supply nozzles from both sides thereof, along the circumferential direction of the substrates, and which supply the inactive gas to the inside of the processing chamber.