In X-ray CT imaging for scanning a subject in the same anatomical region with two kinds of X-rays having different energy distributions, for the purpose of reducing a subject's positional offset between two kinds of tomographic images representing the same slice by a simple control scheme while reducing stress on the subject, a cardiac cycle identifying section 30b identifies a cardiac cycle of a subject 6 by an electrocardiograph 5 or the like, and a scan start time interval setting section 30c sets a time interval from the start of a first scan with first X-rays to the start of a second scan with second X-rays to a time approximately the same as the aforementioned cardiac cycle. A scan control section 30a controls several sections to keep a constant rotation speed of a rotating section 27 and start the scans at the aforementioned time interval. In each scan, projection data over a given view angle sufficient for reconstruction processing for a tomographic image are collected at once.