1. A contour detecting apparatus comprising: a contour model storage section for storing a contour model consisting of a plurality of nodes, which surrounds at least one target object included in a captured image and is used for detecting a contour of said target object; a contour model deforming section for contracting or expanding the contour model by shifting the nodes based on a predetermined rule for deformation; a split-determining section for calculating a distance between two non-adjacent nodes among the nodes of the contour model which was deformed by the contour model deforming section, and determining that the contour model is to be split when the calculated distance is equal to or smaller than a predetermined threshold value; and a contour model splitting section for splitting the contour model according to a result of the determination executed by the split-determining section, wherein the splitting operation is executed in the vicinity of said two non-adjacent nodes.