To accurately simulate the movement of particles in a noncompressed fluid guaranteeing momentum and the preservation of energy.

Concerning the method and the device for simulation with which the character of a system including the fluid is simulated, the non-compressed fluid is regarded as N pieces of particle groups having a mass mj (j=1, 2,..., N) and a velocity uj, a restriction power to be generated is calculated by charging a restriction condition, on which the diffusion of a relative velocity related to each particle is zero, (2) and while using that found restriction power, the movement of particles is calculated (3). In this case, a differentiable integration nucleus j having the character of ∫∫∫ jdr=1 is used for calculation of the restriction power and when the relative velocity of another particle (j) is defined as (uj-uf), concerning a certain particle (f), discrete approximation is performed on the restriction condition of a residual Rf=∫∫∫ f nabla.(Σ (ui-uf) j) dr.