An X-ray CT apparatus 1 comprises a blood-flow information acquisition unit, a correction value calculating unit and a blood-flow image generating unit 24e. The blood-flow information acquisition unit obtains information of a relative blood flow rate in the myocardium of the subject P based on the CT image. The correction value calculating unit obtains a correction value based on the CT image in a concentration transition period defined to be a period from immediately after starting of a continuously injection of a contrast medium into the subject P until the contrast medium injected reaches to the myocardium, increases, and will be in a state where it can be considered that the contrast medium is saturated in a constant value. The blood-flow image generating unit 24e generating a blood flow value image in the myocardium by correcting the information of the relative blood flow rate with the correction value.