A leak check method includes: performing a first inspection of measuring a pressure in an internal space formed by a seal of the substrate holder, while evacuating the internal space, and detecting that the pressure reaches a first pressure threshold value within a predetermined first inspection time; performing a second inspection of closing the internal space that has been evacuated, measuring the pressure in the closed internal space, and detecting that the pressure in the closed internal space does not exceed a second pressure threshold value within a predetermined second inspection time; and performing a third inspection of measuring a pressure difference between the pressure in the closed internal space and a vacuum pressure in a master container, and detecting that an amount of increase in the pressure difference within a predetermined third inspection time is kept equal to or below a pressure difference threshold value.