An objective is to provide an image generation system and program which can implement a realistic image with less processing load and without giving any unnatural feel to a player. It is determined whether or not any obstruction OB intervenes between an enemy character controlled by a computer and a viewpoint VP (or player's character) (or whether or not the obstruction OB exists on a line connecting an enemy character to a viewpoint The present invention is particularly effective when the motion of the enemy character C1 is generated in real time through the physical simulation.