STEAM STERILIZER

PROBLEM TO BE SOLVED: To provide a steam sterilizer capable of preventing a failure in evacuation by keeping an initial lid closed state that a lid is manually closed with a sterilization object housed in a chamber even when the compression margin of a packing is decreased.SOLUTION: The steam sterilizer includes a lid closing device for holding a lid 4 in an initially closed state by engagement between a lid side engaging position and a chamber side engaging portion 31B before evacuation in the chamber 3. In the sterilizer, the lid closing device enables adjustment of the position at which the chamber side engaging portion is engaged with the lid side engaging portion depending on the compression margin of an annular packing so that the initial lid closed state between the lid and the chamber by the annular packing can be a predetermined state when the lid is closed.