1. A method for estimating three-dimensional (3D) positions of human joints using a sphere projecting technique, comprising the steps of: a) marker-free motion capturing a moving figure for obtaining a multiview 2D image of the moving figure, and extracting a 2D feature point corresponding to a bodily end-effector from the obtained multiview 2D image of the moving figure; b) three-dimensionally matching the 2D feature point corresponding to the bodily end-effector, and recovering the 3D coordinates of the bodily end-effector; c) generating a 3D blob of the bodily end-effector by using the recovered 3D coordinates, generating a virtual sphere with a radius that is a distance from a center of the 3D blob to a joint, and projecting the virtual sphere onto the obtained multiview 2D image of the moving figure; and d) detecting a coinciding point of a surface of the projected virtual sphere and the multiview 2D image of the moving figure, and estimating a 3D position corresponding to the coinciding point as a 3D position of the joint.