Climate Change is becoming an increasingly important environmental issue these days. During the past ten years, Tokyo Metropolitan Government(TMG) has developed a proactive climate policy and have led to similar policies in other local governments, as well as the Japanese government. This paper attempts to deal with the research question directed at the roles of TMG and other actors in policy-making process of a specific policy field: What roles had TMG and other stakeholders played in solar thermal policy making process to revitalize stagnating Japanese market? Three data collection methods were used for this research such as document survey, participant observation and interviews. This study clarified the important roles of TMG and other stakeholders in solar thermal policy-making process. It is worth noting that TMG and several actors had strongly promoted its solar thermal policy without adequate support from national government. This study will shed further light on the role of TMG in Japanese climate policy with respect to multi-level governance.