When the inner surface of containers conveyed in an inverted posture is sterilized, the sterilization efficiency can be increased, the amount of sterilizing fluid used can be reduced, the sterilization time and washing time can be shortened, the number of drive components of the apparatus can be reduced and the apparatus can be simplified and reduced in cost. A non-inserted nozzle 20 is disposed at a distance of 1-50 mm below the lower end surface 52 of a mouth of a container conveyed in an inverted posture, the sterilizing fluid is mixed with air and the sterilizing fluid is atomized and sprayed intermittently from the non-inserted nozzle toward the inside of the container.