To evacuate an internal pressure of a container without requiring a long time and to shorten the whole cycle time by keeping the container in an open chamber during each of operations of arranging the container in the open chamber, heating, opening a hole on the container and discharging a gaseous product in the container to the outside.

The container 20 is disposed in a station 14 and the open chamber 12 is closed. When the contents (objects to be sterilized) in the container 20 are heated, steam generates. A desired time later, the heating is stopped and a needle 32 is moved forth with a driving device 34. On the wall of the container 20, a hole is opened by a forward movement of the needle 32 and is made through. Tight closure is present on between the container 20 and the needle 32. A fluid in the container 20 flows in the needle 32 by an internal pressure of the container, presses through a discharge line 68 and is discharged. When the discharge is completed, the needle 32 moves to a back movement position. Because the container 20 is not under pressure, it can be taken out. The cycle time required these operations is shortened.