In the present invention, a nitrogen-free ozone generating unit integrates a plurality of functional means into a single package unit, the functional means including a nitrogen-free ozone generator that is cooled to a low temperature, an ozone power source, a MFC, an APC, a heat insulating cooling water inlet pipe, and a heat insulating cooling water outlet pipe. In the nitrogen-free ozone generator, a heat insulating layer made of a heat insulating material such as an insulator is formed to cover substantially the entire surface of an ozone generator outer frame. A cooling water system is configured to set the temperature of cooling water, which is supplied to the nitrogen-free ozone generator through the heat insulating cooling water inlet pipe, to 5° C. or less and to thereby cool the nitrogen-free ozone generator.