1. An X-ray CT apparatus having an X-ray tube emitting an X-ray, a detector detecting X-rays transmitted through a subject to be examined, and a bed on which said subject to be examined is placed, wherein, after a pre-scan causing said X-ray tube to emit X-rays with said X-ray tube, said detector and said bed at stopped positions, said X-ray tube and said detector are moved relative to said bed to perform a scan over an reconstruction area of an image, comprising: a reconstruction part configured to reconstruct the pre-scan image of said subject to be examined from transmission data detected by said detector during said pre-scan, and also to reconstruct the scan image of said subject to be examined from the transmission data detected by said detector during said scan; a switching control part configured to switch from said pre-scan to said scan; and a scan controlling part, when it is switched to said scan by said switching control part, configured to scan by changing the helical pitch from the stopped position for said pre-scan directly to the position toward an ending edge of the reconstruction area of the image, wherein: said scan controlling part scans at a first helical pitch by which X-rays for a predetermined number of views can be emitted at a starting edge of the reconstruction area of the image, and then, after X-rays for the predetermined number of views is emitted, the scan at a predetermined second helical pitch is controlled to continue.