A semiconductor processing apparatus includes a process chamber to accommodate a target substrate, a gas supply system to supply a process gas into the process chamber, an exhaust unit to exhaust the process chamber, and an exhaust line connecting the process chamber to the exhaust unit. An opening variable valve is disposed on the exhaust line, and an inactive gas line is connected to the exhaust line on an upstream side of the opening variable valve to introduce an inactive gas. A pressure control mechanism is configured to control a pressure in the process chamber by adjusting at least one of an opening ratio of the opening variable valve and a flow rate of the inactive gas during a process in the process chamber while causing the exhaust unit to exhaust the process chamber and introducing the inactive gas from the inactive gas line into the exhaust line.