Endoscopic images and virtual endoscopic images are obtained. Then, an endoscopic image captured at a predetermined position of the anatomical structure is extracted from the obtained endoscopic images, and a comparative virtual endoscopic image virtually generated as if it is captured at a position corresponding to the predetermined position is extracted from the obtained virtual endoscopic images, and the extracted images are associated with each other. A three-dimensional position corresponding to each pixel forming the endoscopic image captured at the predetermined position is calculated based on a three-dimensional position of each pixel forming the comparative virtual endoscopic image. Then, volume data is generated from the endoscopic image captured at the predetermined position based on a pixel value of each pixel forming the endoscopic image and the three-dimensional position calculated for each pixel.
