A program which can dynamically and realistically express an impact which a game character rendered by motion data receives is provided. In bullet ball-related processing (S114), determination is made about whether a bullet ball hits either one of node assigned balls. When the determination is affirmative, a torque at a hit point is calculated as an impact magnitude and the node assigned balls are disposed, through calculation of a rotation angle per frame, to nodes whose coordinate positions are corrected in metaball update processing (S120), density is calculated for each vertex of voxels from a reference position of each metaball towards the minimum direction and the maximum direction of a voxel index of the voxels according to a calculation equation expressing a solid shape in density distribution processing (S122), and vertex coordinates of polygons are calculated based upon density of each metaball at the vertex coordinates of the voxels and a predetermined threshold in marching cube processing (S124).