An object of the present invention is to provide a wind turbine generator and a tidal current generator equipped with a hydraulic transmission with a combination of a hydraulic pump and a hydraulic motor and which has a superior productivity and maintainability. The wind turbine generator 1 has the hydraulic transmission 10 for transmitting the rotation energy of a main shaft 8 to a generator 20. The hydraulic transmission 10 includes a hydraulic pump 12 of variable displacement type which is driven by the main shaft 8, a hydraulic motor 14 of variable displacement type which is connected to the generator 20, and a high pressure oil line and a low pressure oil line which are arranged between the hydraulic pump 12 and the hydraulic motor 14. The hydraulic transmission 10 is at least partially constituted of a plurality of modules (M1 to M7).