3-D models of various types of objects such as a robot body, and a peripheral equipment, a machine, a part (workpiece), of the robot, are stored in an object library in advance. Dimension line data of an edge line of which dimension can be changed, and constraint condition for constraining coordinate positions of apexes which can be changed are also stored in the object library. A model having the shape corresponding to the shape of the object to be used is selected from the object library, and the dimension of the shape is set. The dimension of the selected model is modified so that the shape of the model corresponds to the shape of the actual object. Using the model of which dimension was adjusted, animation motion of the robot is formed on a display screen. With the above arrangement, it is possible to easily set and change object 3-D models relating to a robot motion.