A substrate processing apparatus including a process chamber configured to receive a plurality of substrates oriented in a horizontal manner and vertically arranged with respect to the process chamber, a process gas supply unit configured to supply at least one process gas to the process chamber through a process gas supply nozzle, the process gas supply nozzle along an inner wall of the process chamber in a direction in which the substrates are sacked, an exhaust unit configured to exhaust the process gas from the process chamber, and a blocking gas supply unit configured to supply a blocking gas through a blocking gas injector provided in a circumferential direction of the process chamber such that a flow of the process gas in the process chamber is controlled may be provided.