The purpose of this study was to establish a dynamic, quantitative engineering model for the mandible movement in man’s mastication by reproducing this movement by using a mechanical model and to define the mandible movement controlling mechanism from the viewpoint of engineering. To realize this purpose, WJ (Waseda Jaw)1, a 1 degree of freedom mastication robot, was developed. The following is a description of the mastication robot WJ-1 with reference to man’s actual mandible movement.