1. An image processing apparatus, comprising: a storage unit configured to store a volume image of a three-dimensional region of a subject; a slice image generating unit configured to generate a plurality of slice images corresponding to a plurality of slices each substantially perpendicular to a predetermined reference axis from the volume image; a region extracting unit configured to extract a target region from the plurality of slice images; and a tubular structure extracting unit configured to detect an end point from the extracted region, and to extract a tubular structure based on the end point.