Japan is a leader in life science, and is one of the countries in the world where reproductive medicine is actively practised. This chapter first analyses the overall regulatory framework for research using human germ cells and embryos (germline). Then, it discusses the specific regulations affecting research on human germline genome modification, while considering the clinical research of an egg mitochondrial DNA modifying technique, called AUGMENT. Regarding research involving human germline genome modification, the Japanese regulatory framework is characterized by gaps and inconsistencies. Moreover, it discusses some of the reasons why Japan lacks a key law governing the medical use of human germline, although the Act on Regulation of Human Cloning Techniques is put into force. It points out that a majority of Japanese is not affiliated with religion, and ‘Morals’ is a vague concept in Japanese. Finally, it discusses a possible regulatory reform, considering four provisions relevant to human rights in the Constitution of Japan.