1. An X-ray CT system comprising: an X-ray source for radiating a cone-beam X-ray; a two-dimensional X-ray detector for detecting the X-ray radiated from the X-ray source and made to transmit an object to be examined and for outputting projection data deepening on an amount of the X-ray; scanning means configured to scan the object with the X-ray radiated from the X-ray source within a particular scan range under a desired scan technique involving at least a movement of the X-ray source along a predetermined orbit thereof, thus making the X-ray detector to acquire the projection data generated by the scan; Radon data producing means for producing three-dimensional Radon data distributed three-dimensionally, from the projection data through the scanning means; weighting means for weighting the three-dimensional Radon data based on a weighting function providing a non-constant weight with regard to an acquisition time of the projection data; and reconstruction means for reconstructing the three-dimensional Radon data weighted by the weighting means, based on a desired three-dimensional reconstruction algorithm, so that an image is obtained by the reconstruction.