A granular material is a simulation target, wherein a force acting on each grain is expressed by a potential dependent term and an energy dissipation term. The potential dependent term depends on an interaction potential ϕ between the grains. Physical quantities included in the potential dependent term are renormalization-transformed so that a hamiltonian form expressed by a kinetic energy of the each grain and a potential energy based on the interaction potential ϕ does not change. Physical quantities included in the dissipation term are renormalization-transformed so that a change rate of the potential dependent term and a change rate of the dissipation term become equal. Temporal development of a renormalized granular material is calculated by performing numerical integration with respect to a motion equation of each grain of the renormalized granular material.