To reduce the size of a moisture content for cooling liquid.

This method is executed such that cooling air fed to cooling of a cooler 1 is recovered to a cold air generating chamber 4, consisting of a part of a cooling source, through a recovery piping 11, the temperature of the recovered air is reduced to a value lower than the set temperature of a cooling apparatus 1 through heat-exchange with cooling liquid cooled to a low temperature by a cooling source and having hygroscopicity, and the cooling air is fed to the cooling apparatus 1 through a feed piping 12. In this case, a part of cooling liquid serving as heat-exchange with the recovery air is fed to a low pressure moisture removing device 5 through a piping for removing a moisture content. In low pressure environment, only a moisture content in low pressure environment is evaporated from the cooling liquid for removal, and cooling liquid from which a moisture content is removed is returned to the cold air generating device 4 side and mixed with remaining cooling liquid and serves for manufacture of cooling air again.