To provide an extraction method which permits the water content of microalgae to be completely extracted inexpensively in a short time and in a space-saving manner.

The extraction method includes the step of separating a nutrient solution containing fine alga into the microalgae and the nutrient solution by centrifugal separation, the step of stirring and mixing the separated microalgae and a liquefied water-compatible solvent which is a gas at room temperature and at normal pressure under pressure and extracting a mixture of the microalgae from which the water content is extracted and the liquefied water-compatible solvent in which the water content is dissolved, the filtering step of filtering the mixture, and a first volatilization step of obtaining the microalgae dried by volatilizing the vaporizing matter of the water-compatible solvent from the obtained filtered matter.