PURPOSE: To carry out effective temperature control and sterilization treatment, by bringing hot water heated to a desired temperature in a showered state into contact with a packed food from the top, continuing showering for a given time and subjecting the food to cold water shower treatment.

CONSTITUTION: A desired number of packed foods to be sterilized are placed on a truck, etc. in the retort 1 and placed on the housing stand 3. A proper amount of water is fed from the water supply part 7, air is sent to the steam blow part 4 by the heat medium feed part 6, and it is heated with steam. When air is heated to about 50W80°C, pressure control is carried out in such a way that suction 5 and the removal of air 9 are performed, and warm water is supplied in a shower state from the sprinkler 2. Warm water showering is continued at a desired sterilization temperature for a necessary sterilization time. After the sterilization is over, the warm water showering is changed to cold water, the foods are cooled and after cooling for a given time, the sterilized packed foods are taken out from the retort 1.