To effectively agglomerate and efficiently recover an objective substance from a solution by pressurizing a recovery chamber to make the saturated vapor partial pressure of the objective substance lower than the saturated vapor partial pressure under the atmospheric pressure.

A solution concentration method comprises the steps of: vibrating the objective substance-containing solution ultrasonically and atomizing the vibrated solution into mists in an ultrasonic atomization chamber 4; and agglomerating/recovering the objective substance from the atomized mists in the recovery chamber 5 to separate the objective substance from the solution, wherein the gas phase pressure in the recovery chamber 5 is kept equal to or higher than the atmospheric pressure and the saturated vapor partial pressure of the objective substance is made lower than the saturated vapor partial pressure under the atmospheric pressure.