A 3D model deformation program is provided capable of performing deformation processing of a 3D model using clusters in each drawing period in a video game. A CPU 21 finds for each cluster with which a vertex is associated the product of a weighting matrix expressing weightings representing the degree of association of a vertex in any desired frame with a cluster with which this vertex is associated, a co-ordinate transformation matrix for transforming the local co-ordinate system of the vertex in this frame to a world co-ordinate system, and an inverse transformation matrix which is the transformation matrix of the co-ordinate transformation matrix for transforming the local co-ordinate system of the vertex in the specified frame to the world co-ordinate system and finds an addition matrix by adding these products.