An X-ray CT system comprises an X-ray source and an X-ray detector opposed to the X-ray source with a subject between them. The X-ray detector detects X-rays irradiated from the X-ray source to the subject. The direction in which the X-ray source irradiates X-rays is shifted about the subject. First tomographic images of a predetermined slice thickness representing sections that are orthogonal to a body axis, which links the subject's head and the subject's tiptoe, at predetermined positions of the subject are produced. The X-ray CT system further comprises a parameter designation block in which parameters that define the conditions for producing second tomographic images, and an image processing unit that produces the second tomographic images from the first tomographic images according to the parameters.