In floating offshore wind power generating devices, with the objectives of safety and of suppressing loss during power transmission, there have been requests for installing a transformer in floating offshore wind power generating devices. At such a time, the transformers installed in floating offshore wind power generating devices are agitated by wind and waves, and so there has been the possibility of incurring transformer damage. As a result, in the present invention, the transformer is disposed at the vicinity of the metacenter, which is the center of the tilting of the floating offshore wind power generating device. As a result, it is possible to suppress agitation of the transformer due to wind and waves, optimize transformer anti-agitation measures, and to reduce costs.