As an ROI for display and an ROI for valve observation as well as a projecting direction are input, a volume-rendering processing unit (123a) creates a first image in the ROI for display through volume rendering processing, and the ray-tracing processing unit (123b) creates a second image in the ROI for valve observation through ray tracing processing. An image compositing unit (13) then creates a composite image by compositing the first image and the second image, and the composite image created by the image compositing unit (13) is displayed on a monitor.