A method for scaling a scattered ray intensity distribution in a multi bulbs X-ray CT apparatus configured to irradiate a subject with X-rays from a plurality of X-ray generation sections, respectively and configure a cross-sectional image of the subject by detecting the X-rays passing through the subject. A first difference is achieved, the first difference being the difference between a real data of X-ray intensity achieved by passing of X-rays through the subject, the X-rays being radiated from the plurality of the X-ray generation sections, respectively and an opposed data of X-ray intensity achieved by passing of these X-rays through the subject at the same position in an opposite direction, a second difference between scattered ray intensity included in the real data and scattered ray intensity included in the opposed data being achieved. Primary scattered ray included in the real data of the X-ray intensity achieved by passing of the X-rays through the subject, the X-rays being radiated from the plurality of the X-ray generation sections, respectively are estimated. Primary scattered ray included in the opposed data of the X-ray intensity achieved by passing of the X-rays through the subject at the same position in an opposite direction, respectively, and performing scaling the primary estimated scattered ray intensity distribution on the basis of a ratio between the first difference and the second difference are estimated.