X-ray CT system is provided that reduces waiting time for shuttle scanning, comprising: top-plate moving unit; rotary moving unit; data acquisition system; and control unit. Top-plate moving unit displaces top plate to reciprocate in a direction from a starting point to an ending point and in the direction from the ending point to the starting point. Rotary moving unit drives X-ray radiator radiating X-rays to revolve around the subject. Data acquisition system detects X-rays passed through the subject and to gather projection data. Controller controls at least top-plate moving unit so that, during a scanning with X-rays, while projection data are gathered with reciprocating movement of top plate between the starting point and the ending point and with X-ray radiator being driven to make revolving movement, the duration required for reciprocation of the top plate movement being an integral multiple of revolution period of the revolving movement of X-ray radiator.