In one embodiment, an image processing apparatus includes a difference image generating unit and a display controlling unit. The difference image generating unit generates a difference image by calculating a difference in a second X-ray transmission image from a first X-ray transmission image, the second X-ray transmission image being an image in which a myocardial tissue of an examined subject is not opacified and the first X-ray transmission image being an image in which the myocardial tissue of the examined subject is opacified with a contrast agent that has been injected into a coronary artery. The display controlling unit exercises control so that a predetermined display unit displays the difference image that has been generated by the difference image generating unit.