According to one aspect of the technique of the present disclosure, there is provided a substrate processing apparatus including: a process vessel constituting a process chamber; a first gas supplier provided with a first supply port through which a first process gas is supplied; a second gas supplier provided with a second supply port through which a second process gas is supplied; a plasma generator provided along an outer circumference of the process vessel and configured to be capable of plasma-exciting the first process gas supplied into the process chamber; and a substrate mounting table on which a substrate is placed. The second supply port is provided at a supply pipe extending downward from a position in a ceiling surface of the process chamber located closer to a radial center of the process vessel than the first supply port, and is provided below the first supply port.