According to one embodiment, an image processing apparatus includes following units. The correspondence table describes a relationship between blood vessel contrasts and reference contrast medium concentrations and reference X-ray conditions. The acquisition unit acquires a blood vessel contrast by referring to the correspondence table based on the planned value of a contrast medium concentration and the X-ray condition. The calculation unit calculates a predictive pixel value of a region of interest set on the X-ray image based on the blood vessel contrast. The display unit displays the X-ray image while superimposing a partial image with the predictive pixel value on the region of interest.