A tubular structure, such as a blood vessel, of a subject is extracted from each of a three-dimensional image representing the tubular structure and a three-dimensional intra-tubular-structure image that has been generated from plural tomographic images of the tubular structure obtained by performing tomography on the tubular structure plural times from the inside of the tubular structure along a path in the tubular structure. Further, an arbitrary range in one of the tubular structure extracted from the three-dimensional image and the tubular structure extracted from the three-dimensional intra-tubular-structure image is correlated with a corresponding range in the other one of the tubular structures. Further, a projection three-dimensional image is generated by projecting an image of a specific structure included in the range in the three-dimensional intra-tubular-structure image into the correlated range in the three-dimensional image.
