5 cm 3 and the surface area of the cold head 30 is for example about 10 cm 2 in the ozone chamber only ozone is liquefied under the conditions of a temperature ranging from 75 to 95k and a pressure of not more than 10 torr while making use of the difference between the saturated vapor pressures of the components present in the ozone containing gas the remaining gas mainly comprising oxygen is exhausted by the action of the vacuum pump 27 through a valve 32 an ozone killer 39 a gas refrigerator 40 and a liquid nitrogen trap 38 these devices and or tools being in order connected through a proper piping system 44 at this stage a conductance valve 31 positioned between the ozone chamber 26 and the oxidation treatment chamber 1 is closed while the valves 25 and 32 are opened the ozone containing gas supplied from the ozonizer is cleaned by passing it through the filter 24 for removing fine particulate substances for instance an in line gas filter which can remove 99 9999 of fine particles having a particle size of not less than 0 05 u03bcm after liquefying a predetermined amount of ozone the valves 25 and 32 are closed while the valve 31 is opened to thus communicate the ozone chamber 26 to the chamber 1 for oxidation treatment the temperature of the liquefied ozone is controlled to a level ranging from about 80 to 100k within an accuracy of 0 1k by a temperature control device 35 which is equipped with the refrigerator 29 a heater 33 and a resistance thermometer 34 to.