The Two-Gap theory of Chenery and Strout [7] is based on the aggregation analysis regardless of the different types and qualities of investment of the foreign investors. Especially, previous studies merely focused on needs coming from the invested countries while neglecting the cost of introducing foreign investment and the reaction of investors. As a result, the theory itself may not be appropriate for explaining all kinds of investment needs. Therefore, this research is mainly adapted to respond those ignored demands. First of all, the cost of foreign investment will be introduced in both qualitative and quantitative factors into the traditional model. Also, the needs of the developing host country must be identified. This study provides clarifications of the mutual relationship between the demanded scale and the qualitative and quantitative factors coming from the foreign investors. Consequently, regarding the investing behavior of foreign investors and the applied framework of the game theory, the decision and the influence of the developing country which adopts ”The Foreign Optimum Scale” will be further examined and analyzed.