As an examination for analyzing a myocardial blood flow, myocardial perfusion is known. For example, in the myocardial perfusion, an X-ray computed tomography (CT) apparatus obtains a time-density curve (TDC) indicating a temporal change in a CT value of an aorta and a TDC indicating a temporal change in a CT value of a myocardium from X-ray CT images that are generated by capturing chronological images of a subject to which a contrast agent is administered. Then, by solving a transfer function or a compartment model using the TDC of the aorta as input and the TDC of the myocardium as output, a myocardial blood flow rate is calculated.