Importance of scientific ocean drilling was becoming more widely known in the Japanese scientific community, based upon the results of DSDP/IPOD/ODP by late 80s. Many scientific and engineering discussions took place domestically and internationally, and finally those discussions led the Japanese government to decisively move forward with the construction of D/V Chikyu. Finally, Chikyu was delivered to the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in July 2005. Chikyu was designed and built as a scientific ocean drilling vessel capable of riser drilling in water depths of 2,500 m (future target is 4,000 m class). Chikyu can drill in deeper water and to deeper sub sea floor depths than any other scientific drilling platforms. Chikyu’s large hull makes it possible for a large onboard laboratory, with space for large analytical instruments and facilities. Since the first scientific operation conducted in the Nankai Trough in 2007, Chikyu made significant scientific achievements by IODP Expeditions. Those results are briefly introduced and show a future operation challenge with introducing Chikyu’s general features.