By the microprocessor all functions are automated, and the sterilization cycles are monitored. In other words, all phases such as fill, heat, sterilize, vent, dry and completion are automatically proceeded. At any time, the operator may know the present temperature, the remaining sterilization or drying time, the proceeding phase and the water level of the reservoir by means of the display. If there takes place an abnormal condition, the 6 error messages are given with audible alarm by the self- diagnosis function.