Offshore wind energy resources in Japanese EEZ are now considered to be huge. In order to utilize the huge amount of energy located in relatively deep water areas, Ministry of the Environment, Japan funded a demonstration project on floating offshore wind turbine (FOWT). In the project, two FOWTs have been installed. The first FOWT mounted a 100 kW wind turbine of downwind type, and the length dimensions are almost half of the second FOWT. The second FOWT mounted a 2 MW wind turbine of downwind type, and was referred to as the full-scale model. The FOWTs consist of PC-steel hybrid spar which is cost-effective and are moored by three mooring chains. The half-scale model was installed at the site (Kabashima, Goto Islands, Nagasaki prefecture, Japan) on 11 June 2012. The half-scale model was attacked by a very severe typhoon Sanba (1216). The behavior of the half-scale model during the typhoon attack was recorded, and compared with the computer simulations, indicating the validity of the design method. After a successful demonstration test of the half-scale model, the full-scale model was designed, constructed and installed at the same site. The demonstration test for the full-scale model was also successful. After completion of the demonstration project, the full-scale model was moved to a different site off Fukue island, where future expansion as a floating wind farm is planned. There, the full-scale model is operating as a commercial floating wind turbine, providing valuable data and experience for operation and maintenance toward commercial-scale floating wind farms.