An object having a concavity on a surface thereof is formed by means of a computer. A part of the surface of the object including the concavity is extracted. A spatial part in contact with the extracted surface of the object is formed by dividing the extracted surface of the spatial part into blocks. A large number of lattice-shaped portions is formed by dividing the spatial part into lattices. In a simulation, a gas is flowed into the spatial part in one direction. The motion of the gas is computed discretely for each lattice-shaped portion at each slight time by the equation of continuity and the Navier-Stokes equation. Based on results of the computation, the motion of the gas is visualized by a visualizing program.