Abstract Environmental protection technology plays an important role in a sustainable society, simultaneously promoting economic development and pollution control. This study examines the determinants of technology inventions related to environmental protection in Japan. We use patent application data in a decomposition analysis framework. We find that environmental patent applications increase according to the prioritization of environmental patents by private companies and according to efficiency improvements in patent applications in the public sector. Additionally, patent applications related to emission trading increased rapidly among private companies, mainly due to their increased priority after 2005. The different determinants of environmental technologies between the private and public sectors are useful for formulating effective policies to promote environmental innovation.