1. Strong and Sound Structure This sterilizer, which has a practical medium sized chamber between large and small sized sterilizer and is very effective to load the volumed loads, uses the saturated vapor as sterilant supplied from the built-in steam generator or external steam supply system. The cylindrical chamber with jacket is the most sound structurally and the door is sealed firmly by a locking system with radial levers. It is fully automated in all processes by means of microprocessor. If a trouble takes place, it alarms with digital display and buzzer through the self-diagnosis function, and then stops the cycles. The door system shall consist of a door and an opening/closing mechanism which shall be manually operable. 2. Variable Cycle Programs and Self-Diagnosis Program 4 kinds of optimized basic cycle program for sterilizing general medical instruments are embedded in the controls of sterilizer. Therefore operator can select a proper cycle conveniently for sterilizing a load and change the parameters of program easily according to the sterilizing condition. The self-diagnosis program generates the warning signal, displays the error code on the control panel and aborts the executing cycle for safety automatically in case that any operating error has occurred during cycle executing.