PURPOSE: To realize the high-speed processing of drawing operation by reducing the data volume of an animation and minimizing the number of polygons in each stage of the animation.

CONSTITUTION: A timer 4 is initialized (step 71), and the time is read (step 72), and a synthesis ratio of parameters of respective form functions adapted to this time is obtained (step 74). A parameter corresponding to a reference ratio is generated, and this parameter is transferred to a form generation function processing part 5 to generate and output polygon data corresponding to the parameter. This polygon data is used as model data to perform the hidden face processing by the Z buffer method as technique of normal computer graphics hereafter, and results are displayed as a picture (steps 78 and 79). The loop processing is performed in the same manner till expiration, and the form change of a three-dimensional model is displayed as an animation.