1. An X-ray CT apparatus comprising: an X-ray data acquisition device comprising an X-ray generator and an X-ray detector positioned opposite the X-ray generator such that the X-ray generator and the X-ray detector are rotated about a center of rotation placed between the X-ray generator and the X-ray detector, the X-ray data acquisition device configured to acquire projection data of X-rays transmitted through a subject disposed between the X-ray generator and the X-ray detector, the X-ray data acquisition device is further configured such that a second detector channel width, d 2 , located at each peripheral portion of the X-ray detector as viewed in a channel direction becomes d 1 <d 2 with respect to a first detector channel width, d 1 , located at a central portion of the X-ray detector as viewed in the channel direction or such that a plurality of detector widths, (d 1 , d 2 ,. .. d i ,. .. d n-1 , d n ), provided from the central portion of the X-ray detector as viewed in the channel direction to the peripheral portion of the X-ray detector, are sized such that d 1 ≦d 2 ≦. .. ≦d i ≦. .. ≦d n-1 ≦d n ,the X-ray data acquisition device further comprising a plurality of data acquisition sampling periods at which data acquisition is performed, the plurality of data acquisition sampling periods differing according to channel positions; an image reconstructing device configured to image-reconstruct the projection data acquired from the X-ray data acquisition device; a display device configured to display an image-reconstructed image generated by the image reconstructing device; and a control device configured to control an X-ray irradiation area in a row direction such that the X-ray irradiation area differs according to positions in the channel direction.