A power generating device includes an input rotor that is provided to an output shaft of speed up gears so as to be capable of rotating together with the output shaft, an output rotor that is provided to a drive shaft of a generator so as to be capable of rotating together with the drive shaft, and a one-way clutch that is disposed between the input rotor and the output rotor. The one-way clutch connects the input rotor with the output rotor so as to rotate together with the input rotor and the output rotor when the rotation speed of the input rotor exceeds the rotation speed of the output rotor, and the one-way clutch is configured to release the connection between the input rotor and the output rotor when the rotation speed of the input rotor falls below the rotation speed of the output rotor.