Overview images that represent the overview of a structure (e.g., the large intestine) are generated based on volume data, and displayed on a screen. Points within the overview images and points corresponding thereto in the volume data are set as target points. A target volume that includes the target points and line of sight vectors within the volume data having the target points as endpoints and a movable viewpoint as a starting point are set within the volume data. The directions of the line of sight vectors are changed by moving the viewpoint, and the target volumes are projected onto projection planes perpendicular to the directions of the line of sight vectors to generate detailed images that represent details of the structure in the vicinity of the target points. The detailed images are displayed on the screen.
