Substrate processing apparatus and substrate processing method

A substrate processing apparatus comprising:

• a processing container to which a supercritical fluid is supplied, the processing container being configured to dry a substrate by replacing a drying liquid collected on the substrate with the supercritical fluid;
• a discharge line configured to discharge a mixed fluid containing the supercritical fluid and the drying liquid from an interior of the processing container;
• a density meter installed in the discharge line and configured to detect a density of the mixed fluid flowing through the discharge line;
• a first circuitry configured to calculate a reference density which is a density of the supercritical fluid having a temperature and a pressure that are the same as a temperature and a pressure of the mixed fluid flowing through the discharge line;
• and
• a second circuitry configured to calculate a density difference between the density of the mixed fluid detected by the density meter and the reference density calculated by the first circuitry.