The present invention provides an image generation system and a program embodied on an information storage medium or in a carrier wave which can generate an image in real-time of an object that distorts in accordance with an impact position, with a reduced quantity of data and computational load.There is provided an image generation system which generates an image of an object formed by a primitive surface. It comprises an impact computation section (114) which computes an impact position at which an impact is imparted to the object and a distortion computation section (116) which performs computations for causing the distortion of the primitive surface in the vicinity of that impact position, to generate an image of the object formed by the primitive surface that has been distorted when the object has been subjected to an impact. If polygonal objects are used, at least one vertex that is to be moved by the impact is determined, that vertex is moved to a distortion point, and an image is generated of the object that includes that post-movement vertex.