The recent changes in the energy landscape have been extremely intense and complex, including the global movement toward decarbonization and the growing interest in security and resilience. In this situation, it would be preferable to consider open sharing of information and strategies with multiple stakeholders transdisciplinarily with open data and open-source software. The objective of this study is to clarify whether OSS energy system modelling tool OSeMOSYS and MoManI, which is European oriented application, can handle a model of Japan, where multiple regions are linked with complex interconnections. The basic function of OSeMOSYS is to calculate the configuration of power sources with the lowest cost for target period. In this study, two enhancements were made to this application. Firstly, since there are mechanical limits of ramp up/down rate in actual power generation facilities, new constraint equations were incorporated into model to set upper limits on the rate of changes. Secondly, three types of power supply facilities were arranged into model virtually to connect grids of multiple regions with restrictions. Overall, the optimization results for 2020 roughly reflect the trend in electricity supply by thermal power, hydro power, nuclear power, renewables and others. As for inter-regional transactions, the results reflect regions that receive supply from others (Tokyo, Kansai and Chugoku), regions that send electricity to others (Tohoku, Hokuriku, Shikoku and Kyushu), regions with a mixture of both (Hokkaido and Chubu) and regions with no transactions (Okinawa). The above results show that OSeMOSYS/MoManI can appropriately handle energy system of Japan.