1. A diagnostic imaging support processing apparatus comprising: a nodular region determination unit which determines a nodular region included in an image showing the inside of a subject; a polygonal line approximation processing unit which obtains a plurality of nodes constituting a polygonal line that approximates a contour of the nodular region; a reference position determination unit which determines a position of a reference point; and a circularity computation unit which computes the degree of circularity by using areas of a plurality of regions determined based on the plurality of nodes and the reference point.