The massive black hole candidate at the center of our galaxy and the test of gravity theory

50% of the Nobel Prize in Physics 2020 was awarded to the discovery of the supermassive compact object (candidate of massive black hole) at the center of our galaxy, which was pioneered by American and European groups in the latter half of the 1990s. This article explains its impact on the test of General Relativity at a strong gravity regime. Concerning the General Relativity test, not only the American and European groups but also our Japanese group have been making contributions, using the world largest infra-red telescopes. Our research is also introduced. (author)