An X-ray CT apparatus includes a perfusion data acquisition unit, a perfusion parameter calculating unit and a perfusion parameter display unit. The perfusion data acquisition unit generate perfusion data by exposing an X-ray to the object with injecting contrast medium. The perfusion parameter calculating unit calculates perfusion parameters corresponding to ROIs based on time variations in density of the contrast medium for the ROIs. The perfusion parameter display unit divides a period to be a calculation target of the time variations into plural time ranges and sequentially displays images each including the ROIs. The images correspond to the time ranges and mutually different time phases respectively and are masked so as to make only ROIs at which the perfusion parameters show values displayed.