An endoscope cleaning/disinfecting apparatus for processing an endoscope in a cleaning tank using a diluted chemical obtained by diluting a chemical with hot water in a dilution tank of the present invention introduces the hot water into the cleaning tank immediately before processing, introduces the hot water into the dilution tank after the temperature of the hot water introduced into the cleaning tank falls within a specified temperature range, generates the diluted chemical, introduces the diluted chemical into the cleaning tank and processes the endoscope.
