PROBLEM TO BE SOLVED: To provide a high-pressure steam sterilizer in which internal pressure control of a sterilization chamber using absolute pressure and lid opening/closing control is performed by a simple structure using one absolute pressure sensor.SOLUTION: Switching is performed so that a three-way valve 1d can make an absolute pressure sensor S1 connected to the atmosphere in predetermined timing, for example, before sterilization of an article to be sterilized and after the completion of the sterilization and can make the absolute pressure sensor connected to the inside of a sterilization chamber 1a after the completion of the sterilization of the article to be sterilized. Thus, atmospheric pressure and internal pressure of the sterilization chamber 1a are measured by the one absolute pressure sensor. After the completion of the sterilization, the high-pressure and high-temperature steam is discharged. A control means 5 unlocks an interlock mechanism 13 in timing when a measurement value of the internal pressure of the sterilization chamber approximately agrees with a measurement value of the atmospheric pressure. This makes the lid 1b openable.
