This study focuses on the improvement effect of corporate governance (especially independent monitoring) on firm value. We aim to theoretically identify, by setting up a model, the companies that show greater increase in value as a result of monitoring improvement, and confirm these results empirically. Initially, the tunneling behavior of managers is drawn through the theoretical model in relation to different monitoring levels. Subsequently, the expected cash flow of the company and default probability from those behaviors is also identified. In addition, the numerical solution of the model is drawn in terms of the increase in firm value after the enhancement of the monitoring level; the characteristics of such companies can actually be observed. In other words, this study confirms that the impact of monitoring improvement on firm value is greater in companies with high stock volatility (or with low managerial compensation) and a low level of monitoring during the previous year. Based on these results, this study verifies the relationship between monitoring improvement and firm value empirically, and thus it is expected to contribute to the security selection of corporate governance funds.