A view image of high time resolution acquired in an imaging process of X-ray CT is displayed. In this display, by subtracting a background image obtained by forward projection calculation of a CT image from the view image, background is removed from the view image, and only a focused site is imaged. A transmission image of the focused site showing high display contrast and not easily influenced by a motion artifact can be thereby obtained. Thereby, in an X-ray CT device for diagnostic imaging, degradation of diagnostic ability due to motion artifacts can be prevented.