For the purpose of X-ray CT imaging a heart of a subject with high image quality while reducing stress on the subject, once an optimal cardiac phase has been set by an optimal cardiac phase setting section 30b and a target position in a subject to be scanned when the cardiac phase of the subject is at an optimal cardiac phase is defined at a target position defining section 30c, a transport-starting-cardiac-phase calculating section 30b calculates a transport-starting cardiac phase such that the target position is scanned at the optimal cardiac phase, using the optimal cardiac cycle, target position, scan start position, transport speed of an imaging table, and approach-run time for the imaging table. A scan control section starts transport at the imaging table 4 when the cardiac phase of the subject coincides with the transport-starting cardiac phase, and performs a helical scan with a helical pitch of one or more, for example.