A mammographic CT apparatus includes: a gantry, including a front face plate having an insertion opening for inserting a breast into an accommodation portion; a radiation tube disposed within the gantry; a sensing device disposed within the gantry so as to face the radiation tube, to detect radiation which has been emitted from the radiation tube and been transmitted through the accommodation portion; a driving unit to rotate the radiation tube and the sensing device around a rotation axis set in the normal direction of the insertion opening, at the same angular speed and same direction; and a collimator configured to rotate around the rotation axis synchronously with the radiation tube and sensing device. The collimator is disposed near the accommodation portion, and an irradiation region of radiation emitted from the radiation tube is restricted such that a breast inserted to the accommodation portion is irradiated to the tip.