A technique that includes : a process chamber in which a substrate is processed with a gas; a plasma generator configured to convert the gas into a plasma state; a supply pipe installed at an upstream side of the process chamber; an exhaust pipe installed at a downstream side of the process chamber; a valve installed at a downstream side of the exhaust pipe; and an attenuator configured to attenuate an energy of the gas in the plasma state, the attenuator being installed at the exhaust pipe at a position closer to the valve than the process chamber, or installed at an upstream side of a connection between the supply pipe and the process chamber.