a high-pressure processing step of processing an object under a high pressure by bringing at least a high-pressure fluid into contact with the object in a high-pressure processing chamber under the high pressure;

a displacement step, performed subsequent to the high-pressure processing step, of replacing the high-pressure fluid in the high-pressure processing chamber with a supercritical fluid; and

a depressurizing step of decreasing the pressure of the supercritical fluid in the high-pressure processing chamber to atmospheric pressure, wherein the depressurizing step includes a substep in which the pressure in the high-pressure processing chamber is maintained substantially constant to suppress or recover a temperature descent caused by an adiabatic expansion during the depressurizing step, and wherein the temperature in the chamber during the depressurizing step is controlled to be maintained above a temperature achieved by an adiabatic expansion, the adiabatic expansion starting from the pressure and temperature at the end of the high-pressure processing step, wherein the temperature in the chamber during the displacement step and the depressurizing step does not exceed the temperature at the end of the high-pressure processing step.