OBJECTIVES: The purpose of this study is to clarify the spread with prescription of generic drugs and the shift from brand drug market by using nationwide administrative data. METHODS: For the sample, out of 30 drugs seen as the parameter for generic drugs in France, 27 have been selected after considering their availability in Japan. For those drugs unapproved in Japan, they were replaced by other drugs with the same effects, and anticancer agents as well as radio contrast agents were added. New drugs listed to National Health Insurance list around the same time were also included for comparison. Database was created by extracting the data of patients who were prescribed those drugs from DPC/PDPS data collected between 1st April 2010 and 31st March 2012 at 1139 of acute care hospitals in Japan. Hospitals were classified into five categories (university, private, publi, social insurance group, and others). SQL Server 2008 R2 was used for data handling, R for data analysis, and ArcGIS for statistical analysis of geography. RESULTS: Generic drugs were least used amongst almost all types of drugs in university hospital and social insurance group. For prescription of generic drugs, private hospital was the most proactive, followed by public hospital. It was revealed, thorough comparison between 20% of medical care institutions that are the most proactive towards introduction of generic drugs and 20% of the least proactive, that the shifting progress was slower in bigger size medical care institutions. CONCLUSIONS: This study indicated that for effective promotion of generic drugs, it is important to establish plans for changing the policy of medical care institutes, which are amongst the bottom 20% of introduction rate, where a policy maker does not shift to generic drugs even in the area of expensive drugs such as anti anticancer agents and radio contrast agents.