Prior to transfer of an wafer W, a mixed gas is being generated and exhausted, thereby fluctuation of concentration and temperature of a solvent component at the beginning of gas introduction into a chamber 3 is suppressed. A step of gelling after the wafer W is carried into an aging unit is divided into several steps. Until a temperature of the wafer W reaches a predetermined treatment temperature, an average concentration of the solvent component in a mixed gas is gradually raised relative to the temperature of the wafer W. Thereby, immediately after the wafer W is transferred into a sealed chamber, the gas of the solvent component is prevented from condensing.