It is known that the Lattice Gas Automata (LGA) models simulate a sound wave process. Moreover, it is proved that the LGA model corresponds to the hyperbolic equation. The computer simulation show that a wave profile varies with time: the profile amplitude reduces, the profile width increases. This suggests that the particle interaction rules simulate a diffusion process in addition to the wave process. In this paper, the availability of the diffusion effect is demonstrated by computational experiments with a simple LGA model.