advertisement Mean field approximation Advertisement is the very important factor to increase the purchase intention of the customer in the market. Usually, the advertisement campaign is done at TV, newspaper and other medias. We consider the advertisement effect as an external force to the purchase intention as follows, where D$_{ij}$ is the factor for the direct communication and P$_{ijk}$ is the factor for the indirect communication. Because of the term of the indirect communication, this equation is a nonlinear equation. To solve the equation (12), we introduce here the mean field approximation for simplicity. Namely, we assume that the every person moves equally so that we can introduce the averaged value of the individual purchase intention. where introducing the number of potential audience N$_{p}$ . We obtain the direct communi- cation term from the person who do not watch the movie as follows, where D nn is the factor of the direct communication between the persons who do not watch the movie at the time t . Similarly, we obtain the indirect communication term due to the communication between the person who do not watch the movie at the time t , dI$_{i}$ ( t ) dt = − aI$_{i}$ ( t ) + A ( t ) + ∑ j D$_{ij}$I$_{j}$ ( t ) + ∑ j ∑ k P$_{ijk}$I$_{j}$ ( t ) I$_{k}$ ( t ) (12) I = 1 N$_{p}$ ∑ j I$_{j}$ ( t ) (13) ∑ j D$_{ij}$I$_{j}$ ( t ) = N$_{p}$ 1 N$_{p}$ ∑ j D$_{ij}$I$_{j}$ ( t ) ⇒ N$_{p}$ − N ( t ) N$_{p}$ ( N$_{p}$ − N ( t )) D $^{nn}$I (14) 7