It is an object to prevent a poor X-ray CT image due to scattered X-rays. An X-ray CT scanner (100) uses an X-ray detector (4), etc., to scan (F1) an object (3) to obtain X-ray transmission image data, and estimate (F3) an X-ray absorption coefficient distribution inside the object (3) based on the scanned X-ray transmission image data. Next, the X-ray CT scanner (100) performs a Monte Carlo simulation on a simulated object (3) having the X-ray absorption coefficient distribution estimated, and estimates (F4 and F7) a point spread function or scattered X-ray distribution derived from the object. Then, the X-ray CT scanner (100) corrects (F5 and F8), based on the point spread function or scattered X-ray distribution estimated, the X-ray transmission image data, and finally creates (F6 and F9) an image of the X-ray absorption coefficient distribution of the object (3).