Abstract: Medical wastes are placed in a medical waste container which is then placed in a closed apparatus body. The container is heated by a heater so that the medical wastes are sterilized and melted or softened. The container containing the medical wastes is then compressed and molded by a compression device. The compression-molded product containing the medical wastes and the container is then discharged from a door of the apparatus body. Alternatively, medical wastes are heat-sterilized by operating a microwave generator. The microwave generator is controlled by detecting the concentration of the combustible gases contained in the exhaust gases discharged from a closed apparatus body, the concentration of hydrogen chloride gas and/or a ratio of reflected power to incident power by using a power monitor connected to a waveguide of the microwave generator. At the same time, hot air can also be circulated.