I am an observational astronomer studying the early growth history of supermassive black holes (BHs) using large ground-based telescopes and space telescopes. Since my PhD years at National Astronomical Observatory of Japan, I have been deeply involved in the Hyper Suprime-Cam Subaru Strategic Program, a wide-field survey program of the 8.2-meter Subaru Telescope. My current interest is to understand how massive BHs formed and grew within the first billion years of the Universe, and how it is related to the growth of host galaxies. I have been leading several projects of the James Webb Space Telescope, in which we target representative BH populations in the early universe.