This paper is an attempt to use vision-pattern recognition technique to analyzation on a hidden rigid body motion. Specially shaped rod, rigidly connected to the hidden body is extended to the ouside of hiding object so that a camera may catch the motion data. Every motion can be described with translatio and rotation. But translation can be explanied with ratation with a infinitly far centroid. Motion analysis is to find the instantaneous centroid and ratation angle. With this theory jaw motion is analyzed in this paper.