PROBLEM TO BE SOLVED: To provide a sterilizing apparatus that can prevent steam spouting from a relief valve and generation of noise and vibration from piping during transition from a sterilization step to a cooling step.SOLUTION: A treatment tank 3 accommodates an object 2 to be treated and stores water. Circulation means 9 circulates the water stored in the treatment tank 3 between the treatment tank 3 and a heat exchanger 8. Steam supply means 10 supplies steam to the heat exchanger 8 to heat the water circulated by the circulation means 9. Cooling means 11 supplies cooling water to the heat exchanger 8 to cool the water circulated by the circulation means 9. Compressed air supply means 13 is provided which supplies compressed air to the heat exchanger 8 after the steam supply to the heat exchanger 8 by the steam supply means 10 is stopped and before the cooling water supply to the heat exchanger 8 by the cooling means 11 is started.
