An automatic pressure control device that controls a pressure in a processing container to which a source gas for forming a film on a substrate is supplied, includes: a vacuum exhauster configured to vacuum-exhaust a gas in the processing container; an exhaust path connecting the processing container and the vacuum exhauster; and a butterfly valve including an annular valve seat having an inner wall surface and a valve body configured as a plate-shaped body. The valve body is rotatably installed to the valve seat via a shaft and configured to change an opening area of the exhaust path by being arranged to be inclined and changing an inclination angle of the valve body. The butterfly valve is configured to control the pressure in the processing container by changing the inclination angle of the valve body based on a result of detecting the pressure in the processing container.