A substrate processing apparatus of processing a substrate by using a processing fluid in a supercritical state, the substrate processing apparatus includes: a processing container in which the substrate is accommodated; a supply line connecting the processing container to a fluid source configured to send out the processing fluid in the supercritical state; a discharge line configured to discharge the processing fluid from the processing container; a control valve interposed in the discharge line; and a controller configured to control a pressure in the processing container by adjusting an opening degree of the control valve. In a circulation process in which the processing fluid is supplied to the processing container from the supply line, the controller is configured to adjust the opening degree of the control valve such that each of a pressure-lowering step and a pressure-raising step.