A three-stage carrier is transported to an irradiation room by transporting means and is irradiated with gamma ray sources installed on ray source rack such that a product loaded therein is treated. The three-stage carrier includes a central container in a center of the three-stage carrier； an upper container formed on the central container； and a lower container formed under the central container. Here, the central container, the upper container, and the lower container are partitioned by septum, a height of the three-stage carrier is greater than a height of the ray source lack, and the central container has a height greater than a height of the upper container or a height of upper container. The better quality stability through uniform sterilization and the improved energy utilization efficiency and productivity, the reduction of cost may be achieved
