A processing apparatus includes: a processing container configured to accommodate a substrate; a storage tank connected to the processing container via a gas supply pipe; a pressure sensor configured to detect a pressure in the storage tank; a valve provided in the gas supply pipe between the processing container and the storage tank; and a controller configured to control an opening degree of the valve based on the pressure in the storage tank detected by the pressure sensor. The controller is further configured to control the opening degree of the valve to make a drop amount of the pressure become equal to a set discharge pressure, the drop amount being calculated by subtracting the detection value of the pressure sensor in a state where the valve is opened, from the detection value of the pressure sensor before the valve is opened.