1. An X-ray CT system which includes an X-ray source and an X-ray detector opposed to said X-ray source with a subject between them, said X-ray detector detecting X-rays irradiated from said X-ray source to said subject, and said X-ray source being rotated about said subject and moved in order to produce a plurality of first tomographic images representing sections that are orthogonal to a body axis, which links said subject's head and said subject's tiptop, at predetermined positions of said subject, said X-ray CT system comprising: a parameter designating device for designating conditions for producing second tomographic images that represent predetermined sections parallel to said body axis; and an image processing device for producing said second tomographic images from said plurality of first tomographic images according to said parameters.