An X-ray tube and a flat panel X-ray detector (FPD) are constructed movable parallel to each other in the same direction along a body axis which is a longitudinal direction of a patient. The X-ray tube intermittently emits radiation and the FPD detects radiation transmitted through the patient irradiated intermittently whenever the X-ray tube and FPD move every pitch. X-ray images O1, O2, ..., O1, ..., and OM are decomposed for every pitch noted above. The decomposed images are composed for each projection angle to obtain projection images P1, P2 and so on. Therefore, a sectional image with a long field of view in the longitudinal direction can be obtained by carrying out a reconstruction process based on the composed projection images.
