An X-ray CT apparatus comprises a blood-flow information acquisition unit, a correction value calculating unit and a blood-flow image generating unit. The blood-flow information acquisition unit obtains information of a relative blood flow rate in the myocardium of the subject 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 start of a continuous injection of a contrast medium into the subject until the contrast medium reaching the myocardium increases and is be in a state where it can be considered that the contrast medium is saturated at a constant value. The blood-flow image generating unit generates a blood flow value image in the myocardium by correcting the information of the relative blood flow rate with the correction value.