A differential-image creating unit creates a three-dimensional image on which an artery is highlighted and a three-dimensional image on which a tumor is highlighted. An image compositing unit combines the three-dimensional images to composite an image. A display control unit displays the composite image on a monitor. Moreover, when compositing an image, the image compositing unit composites the image such that a tumor nutrient blood-flow inside and outside tumor is to be displayed in respective different colors. Furthermore, a blood-flow quantity inside tumor measuring unit calculates a blood-flow quantity inside tumor and a ratio of the blood-flow quantity inside tumor to a tumor volume, and the display control unit displays the blood-flow quantity inside tumor and the ratio of the blood-flow quantity inside tumor to the tumor volume. Accordingly, information that is meaningful for determining malignancy of a tumor can be provided.