To perform circulatory cleaning and sterilization without requiring any dedicated tank by supplying and storing water or chemical into a liquid storing section formed at the lower part of a thermally insulated tank and circulation supplying the stored water or chemical to a cleaning liquid ejection pipe located at a specified position of the thermally insulated tank through piping and a circulation pump.

When sterilization is performed using a chemical, an automatic control valve SV3 is opened to inject hot water by a supply pump 21 or 22 into a liquid storing section 1a formed at the lower part of a thermally insulated tank 1 and then a specified quantity of concentrated liquid of acid or alkaline sterilization chemical is inject into the liquid storing section 1a. Subsequently, a circulation pump 23 15 started to perform showering of hot water containing the sterilization liquid for a predetermined time repeatedly from a cleaning liquid ejection pipe 11 located at the ceiling part. Since the lower part of the thermally insulated tank 1 is utilized as the liquid storing section 1a and cleaning is performed by circulating water or chemical stored therein, CIP cleaning can be realized by simply fixing a controller incorporating the circulation pump 23 and chemical supply pumps 20, 21, 22.