Recently, in Japan, local authority management has become difficult in many regions where population decrease, declining birthrate and a growing proportion of elderly people are seen. Geographical inequality has increased remarkably due to the progress of centralization to the Tokyo Metropolis. In order to overcome these problems, the Japanese government is promoting major structural reforms known a “Sanmi ittai no Kaikaku”. Therefore, independence from the central government is necessary in finance, and improvements in the efficiency of administrations and finances are required. In this study, socioeconomic data of local authorities including the population and the financial conditions were used as indexes of local authorities in the Shikoku region. The conditions of the local authorities in Shikoku were explained from various viewpoints. Next, the effect of municipal merger, called “the Great Merger of the Heisei Era”, was verified by applying both indexes before and after the municipal merger. First, the status quo of the region was clarified by analyzing the data in detail. Local authorities in the Shikoku region were classified based on conditions of management. The administration of local authorities in each area of Shikoku was classified by using these indexes and a model to evaluate these authorities was developed. Change in the municipal merger was verified by applying both indexes before and after the merger to this diagnostic model. As a result, many regions were found where the administration of local authorities was improved by the municipal merger, but there were also regions that became worse. Therefore, mergers are not effective for all regions. Due to the situation that some mergers are successful and some are not, it is necessary that mergers should be well planned in advance. Mergers should not be done purely due to geographic location. JFL classification: H11, R15