In offshore wind power generator devices, with the objectives of safety and the suppression of loss during power transmission, there is the requirement of installing a transformer within the offshore wind power generator devices. When doing so, an increase in cooling performance of oil-immersed transformers used in the offshore wind power generator devices is called for. To solve the problem, an oil-immersed transformer housing in a tank a core, a coil, and insulating oil that cools and insulates the core and coil is installed below the sea surface within a wind power generator device, and the structure is such that the tank is immersed in liquid. As a result, greater compactness of the oil-immersed transformer and the offshore wind power generator device is possible by means of increasing the cooling performance of the oil-immersed transformer used in the offshore wind power generator device.