In the X-ray CT system according to an embodiment, a control means displaces and images imaging regions in the subject by controlling a top board driver and an imaging means such that the X-rays are projected onto the subject every time a top board is moved by a predetermined transfer amount. An acquiring means acquires projection data of the respective imaging regions. A reconstruction means, based on the projection data, reconstructs tomographic images for each predetermined size of a reconstruction region. In the scan control mode, the control means outputs the transfer amount corresponding to this mode to the top board driver. In the reconstruction control mode, the control means outputs the size of the reconstruction region corresponding to this mode to the reconstruction means.
